Hi!

I just purchased World of Goo. Apparently, I have to build some structures using the goo balls so the goo balls can find the exit. The first few levels were easy. But now I am not sure what I am supposed to do. Whenever I start the game, it starts the same level, Chapter 1, Impale Sticky or some such. I build something, the goo balls vanish through the tube, and when it says 18 of 26 collected or some such, nothing happens. What am I supposed to do?