Here is the start of one of the earlier levels. You will build a bridge to the intake pipe on the other side of the chasm.
You start off with a base, on which the Goo balls you need for your bridge are moving about. There are more Goo balls on the other side. They are sleeping now, but they will awaken when your bridge reaches them.
Your goal for this level is on the lower right. Here you need to collect eight balls of Goo. If you are good enough, you can collect more than that. The excess is sent to the World of Goo Corporation™, where you can make towers out of them.
The bangs from the sign at left tell you that you need to read the sign.