Pull the backrest on your futon bed forward until you hear a "click" or so that you can release the latch on the backside of the futon sofa.
Push the backrest all the way back going in the opposite direction until it is parallel to the ground and clicks.
Extend the footrest portion of the futon sofa until it clicks and until the legs are secured on the floor. The horizontal portion should be parallel with the floor.
Place the extra cushion on the foot rest portion of your extended futon sofa bed. Some models do not come with an extra cushion, but instead come with the cushion already attached.