Put together the two halves of the back of the futon seat by sliding the open ends of the tubes into each other. Secure them in place using some of the shorter bolts that come with futon kit. Tighten the bolts with the Allen wrench that came with the futon kit.
Put together the two halves of the seat of the futon seat the same way you assembled the back.
Set the arms of your futon on the ground, about as far apart as they'll be when the futon is fully assembled. Attach the stretcher bars -- the components that look like beams -- to the arms using the longer barrel bolts and barrel nuts. Fasten the nuts just enough to get a secure hold, but don't tighten them down yet.
Attach one hinge assembly to each side of the arms. Use the lock nuts and flat washers that came with your kit.
Set the futon seat in place and attach it to the hinge assembly using some of the shorter bolts that come with your kit. Attach the back using the same method.
Tighten down all nuts using the Allen wrench and crescent wrench that were included with the futon.
Set your futon mattress in place.