Easy conversion is a very important feature regarding sofa bed and futon furniture design.
Bifold metal frames generally have easy to use "clic-clac" hinges. First of all the hinge allows the front of the frame to be tipped back. When the deck has a gentle nudge that action releases a clip so that part can lay flat. Hence it becomes a bed.
Lift the front section again until it engages the clip. Push down and it makes a reclining sofa. Do this another time, lift the front upright and nudge again so a second time. Then as before push down and it's a sofa and where you started.
Trifold metal sofa beds also have relatively easy conversion. Pull from the front and the sofa will become a bed. Bed to sofa is done by lifting the seat section and pressing down. The frame will concertina to become a safa again.
Wooden frame conversion
Not as easy as the friendly metal frames. There are two types of wooden frame regarding the way they convert. Firstly trifold frames have 3 sections that fold across their width, twice. Because the futon mattress is quite heavy it can make conversion more easy when it is taken off. Either way the frame pulls from the front and the sofa bed becomes a bed.
The reverse isn't an easy conversion. Again the futon mattress can be removed to make the process easier. But the "link or hinge" between the 2nd and 3rd section has to be lifted. Then from the front of the frame push back to become a sofa.
A bifold wooden frame is a little easier. The frame will convert from the front by gently lifting the seat section and easing forward. The reverse has to be from the rear. Lift up until it engages. Then from the front nudge forward until it is safely upright.