I do live in a urban-ish area so trees that I can use for branches do not belong to me. For visual instructions (photos) i will be using drawn pictures of actual photos. i did make this once at a camp. I was going to take pictures of my wonder creation but i sadly left my camera at home. again.
Step 1: Getting the Legs
Get 3-4 big rocks and having them about the same size. Get the 2 biggest ones and put them so you can fit in the between them. So you head should touch one and your feet should touch another. Now move them in about a foot each so on rock should be where your head is and the other should be where you ankle is. If you have 3 rocks, put the last one in the middle. If you have four put, them evenly in the middle. This should help the frame hold your weight. The more rocks the better.
You may not find rocks with flat tops. Find the flatest ones and put dirt on the top and even it out. In addition to level surface, it also gives a bit of bounce :)
If you can't find rocks in general, a mound of dirt works just as well.
Step 2: Making the Frame
Get as many branches that are longer than you and have about the same thickness as the rest. Lay them across the rocks so the sides of the rock are parallel to the branches. This is the frame. The more branches you have laying across, the stronger it is. Tie them together so they don't separate or fall off the rocks. Use rope or vines.
Step 3: Making the Bed
Lay short branches across the bed so you cover the gaps left by the frame. Try and tie those to the frame so they don't fall off when you try to get on the bed. I suggest making a second as this will be stronger. If you can't do this step because there isn't enough material, you can skip it and just lay on the bed frame. It work's just as well.
Step 4: Additional Stuff
You could put leaves on top of the bed to give comfort if you have clothes. if you don't, you can put grass or deer skin if you caught one. If you are really cold, put leaves under the frame in between the legs so it keeps the heat in. Do that with leaves on top of the bed and it's almost like a bed at home. You could try putting dirt if leaves and grass are unavailable. Try to keep some distance from your body to the bed because the bed will be hard and you will wake up with back pain if you don't.