It's actually really easy if you think about it... all you need are 1 hinge about halfway down each of the vertical supports (so they can fold), and two hinges on the ramp (one up top, and one halfway down), so that it can fold up as well. Then just put a couple 2x4s on each section that you can 'swing' into place so as to support the hinged points.
if you don't understand, just ask me i'll elaborate.