You have to pay attention to all stickers on each piece. If you don't know what I am talking about I recommend to turn your cube by 1/8 turn, so that you are halfway through a turn. Then use a screwdriver to pry out one of the middle pieces (not the pieces that are sticking out).
Once you get the first piece out, pull the remaining pieces off the cube. I want you to study each piece and see how many stickers are on the various types of pieces that were once your cube. Now try to put your cube back together solved. This is not so that you can cheat, but so that you can better learn how to solve a scrambled cube. Once your cube is back together in the solved state, then scramble it up again.
The idea is to realize that the top layer is made up not of 9 green stickers, but rather of 8 movable pieces (4 corners and 4 edges) as well as one central piece that spins in place.
You must realize that you are not trying to make 1 side green at first, that is not the goal at all. You are actually trying to place the 8 pieces that all have green stickers, next to the green center piece (the one in the center of a face that is green) such that the pieces all go into their eventual solved locations.
If my message doesn't make much sense, then take your cube apart the way I described. It will make much more sense after that. You cube will not be broken, I can assure you they are quite strong. But you need to understand that a cube is not 54 stickers, but rather 20 moveable pieces that move all over the cube, and 6 center pieces that spin in place in the center of each face. Taking your cube apart will make this completely clear.
Chris