Segufix...well...I am not sure if it's my favorite toy, most certainly the problems they caused (general idea was "Copyrights", but you couldn't help thinking there was more to it) has changed my attitude towards it. It's still a nice item to have and to use.
I bought my first complete system used for a significantly lower Price. You can be lucky to get a Segufix on Ebay nowadays, but most of the time it's not cheap. There are too many people who want one. And I would recommend to think twice before buying a used one. Most of the time the price for the used is very close to the price for a new Segufix. And if you want a new one...well....ask me. I can offer it.
I would like to describe the parts first and then tell you how to use them.
All the belts are made of some kind of webbing, just like the webbing that is used on shades. The belts are about 1.8 inch wide and approx. 1/6th inch thick. All holes in the belts are surrounded by metal, so there is no way they are going to tear out. The hand- and ankle restraints are padded just like the thigh Restraint, so it is not likely you get any bruises. Can't be because otherwise they wouldn' use it in hospitals.

The locks are a bit strange. In the brass pins there is a groove at one end in which two metalpieces fit that are in the lock. Those metalpieces are so easy going that gravity alone lets the lock lock. When you put the magnet on the lock the two metalpieces are moved from the grooves to the side using the magnetic force. Now you can lift the lock together with the magnet from the pin. If you start pulling to early (and thus pull the metalpieces against the pin) the small force of the magnet is not enough to move the metalpieces.
At every part of the belt where you might want to fit a pin the belt is doubled layered. One layer is with the holes, the other one without. When you want to fit a pin here you just slide it in between the two layers so that it comes out through the hole. This way the pins don't fall out.
The magnet is nothing special, it's just a medium strong magnet. You can use other magnets like from a magnetic pinwall or from a loudspeaker. Due to problems concerning magnets and heart pacemakers and due to problems with patients getting free with a spare magnet (like from a pinwall) Segufix has changed the locks. They new ones have four magnets, two or which are turned so that you have 2 southpoles and 2 northpoles facing the same way. That's not copied that easy with a pinwall magnet.

After looking at the parts I decided that it is about time to get to the practical part. I attached the waist belt, the thigh restraint and the foot restraints to the bed. Doing so you place the particular belt around the sides of the bed or whatever you find appropiate and lock them with one of the locks at each side. I think you can imagine how that is done.
Then I got onto the bed and started to lay the fetters on beginning with the feet. I placed my ankles in the restraints and locked them. The other end of that belt can now be attached to the locks that keep the other belt to the bed. I chose to use a tighter attachment and placed the belt of the restraints through the
loops  of the other belt and attached them to the locks that keep that belt to the bed. Doing so all you have left is a small bit of movement. Definitivly no more than 2 inch. And that's fine, don't you think ? (Note : to have even less movement I recommend using a Segufix-Akut-Anklerestraint instead). Next I closed the thigh Restraint. There is nothing much to tell about that, you just take the belts attached to the middle of that bed-belt and lead them up between your legs. You then place one belt through the two loops

left of your legs and one through the two loops right of your legs and attach them to the lock  securing the whole belt to the bed. (Note : the new Segufix thighrestraint is a bit different, it's not such a fuzz. It's just two big cuffs sewn onto the wide belt).
Next thing you need to fasten is the waist belt. This has got a quite wide belt (6,7 inch)  with which it is layed onto the bed and fastened to it. The end of that belt is reduced to the size the other belts have got, so there is no problem fastening that to the bed. Attach the shoulderharness to the mainbelt by slipping it though the approbiate loops.  Before you close the waist belt you should attach the additional belt to the shoulder harness. On one side it is simply slipped onto the shoulder Harness by a loop. You place the additional Belt around the bedstead and simply place it on the other side of your head. After that you place the two belts of the shoulder harness over each other and attach then together with the two ends of the waistbelt. Next you fix the two other belts of the shoulder harness coming from under your arms to the pin that is located on your breast. Now you can also secure the other side of the additional belt to the harness by sliding it through a loop on one side of the shoulder harness and pulling it towards the top of your bed and locking it there. (Note : this is again the old version. The new version of the additional belt is made of two belts. One for each shoulder.)

Afterwards you should secure the side positioning straps. Those are two short belts that are fastened to a loop on the side of the waistbelt . The other end of those belts is locked together with the part of the belt that is attached to the bed. These sidebelts had been detachable in older versions, now they are sewn on. There was some kind of problem with people not using them and patients hanging at the waistbelt over the side of the bed.

This finishes the easy part. Now we have to secure the hands too. From what I discovered there are a number of ossibilities. There is- apart from the loop to which the side straps are fastened- another one on each side of the waist belt. I am not sure what these are meant for, but you could use them to fasten your hands to. Bit of a uncomfortable position, but it works. I guess the far more likely point to fasten your hands to are the two loops on each side of the wide belt laying on the bed.
. You can see that on the other pictures  too.
The question remaining is how do I get out when I closed the hand restraints ? (All those of you who have got someone to strap you in do not need to read this) And how do I close them anyway if I can't reach the pin ? You can only move the hands about 4 inches , there isn't more freedom here.
I thought about this a bit and I think I have found a solution that is equally secure and easy.
You can attach the key to the loop where the side belt is attached to the waistbelt ( I took a "Kabelbinder" for that. Not sure what's the translation for that. I am talking about those plastic-straps that are used to fasten some cables together. Other types of those are used as handcuffs too. The type I am using can be opened, quite in contrast to the normal type).
Then you secure one hand to the loop on the wide belt (you still have got one hand left to do that). After that you take the last restraint and place it on the other wrist and lead the belt attched to the restraint through the loop of the wide belt.
Then you take that belt and "throw" it over to where your other already restrained hand is. You can only just get a grip on that belt since you do not have more movement left. Now you turn the hand you are about to restrain in such way that you can stick the pin on that restraint through one of the holes of the belt. Last thing to do is to place the lock on the key (you attached that to the waistbelt). It will stay there, the magnetic force is strong enough. Again you need to twist you wrist a bit to move the restraint in such a way that you can stick the pin (which is attached to the restraint) into the lock (which is attached to the key). When you have done that you need to slide the lock of the edge of the key. When you try to pull the lock and the pin from the key the lock will stay attached to the key, so you need to slide it away. And that concludes our tieing.
And now...well...nothing more. Try to get out of that. You won't be able to. You are not supposed to anyway. Well of course you can....and that's a bit of disillusion...but then again you want to get loose in case something happenes. Like the house is on fire or something like that. I agree that not beeing able to get out is better, but you need a second person for that. Or you might use the old key-in-the-iceblock method, but I don't like that.
To get loose again all you need to do is move your hand again in such a way that you can place the lock on the key. Pull the restraint and the pin away from the lock and you're free again. This might need a little practice but with a little exercise you can do this with 100%. You might need two or three attempts, but that's O.K. To be really on the secure side you can attach a second key on the loop of the other side belt.
Possibly a even better idea is to use the Segufix 2204 restraint for the wrists. This is thought to restrain wrists to the armrest of a wheelchair. These have velcro on two parts. Just close it (using the velcro) on both wrists and they will look like bracelets. Now open the outer velcro flap, place it through the loop on the waistbelt and close it again. With the other hand that's a bit more difficult, but you can use a normal waistcuff to help you close the 2204. I's both only velcro. But it's surprisingly tough.

Yea, I can hear you asking..." much for the technicality, what about the feeling ?"
I can only say : GREAT. You almost can't move your feet, neither your legs. You can't turn. And you can't sit up. Depending on how tight you made that additional belt you can lift a bit, but with a relatively loose setting you can only get your shoulder about 4 inches up. And of course your hands are useless.
I have tried several times to sleep tied up that way, but I didn't get a good sleep. I guess that's because I tend to move around in the bed a bit and with this configuration this simply isn't possible. When I'm doing a solo session usually I unstrap myself after some hours. That's different of course if it's no solo session.
I would have some thoughts about improvement though. Even if Segufix most probably won't fulfil them. (Which they most probably won't do since I will not tell them my thoughts). I would like to use the waistbelt solitary. You know something like wrists restraint to the waistbelt. That might look a bit like this one from Humane  or like one of these :
This one has the wrists attached to the waist allowing no freedom of movement.
I think this is the best version since here you can adjust the distance between the wrist and the waist. You can restrain the arms right to the waist or allow up to 12" of movement.

The second thought I have got is that the ankle-restraints should be designed so that they may be attached to each other creating a hobble like the one above or like this one :  . You should be able to do something like this with the wrist-restraints which could look like this : .

The third thought I had is that the thigh-restraint should have metal loops instead of the webbing-type it has got. Makes it easier to fit the belt through. That was a old thought of that Segufix has changed the way the thigh restraint looks like it's fine. Even though they didn't use my idea......