GoNNER is broken up into four worlds. Each world is comprised of four normal levels, a shop, a boss level, and a secret area. The normal levels begin with one small level and then increase in size and difficulty. After completing all four normal stages you will have a chance to visit the shop before entering the boss stage.
Each boss stage contains a boss and several regular enemies seen in the preceding levels. Once the boss is defeated, the regular enemies will be killed automatically, and the exit worm appears. There is then a short visit with sally between most worlds, wherein she offers you help.