During a single player game there is an iceberg at the right side of your screen. If you shoot enough, you should find a spot on the iceberg that you can put a hole in. Once this is done, the iceberg will sink.
During single player mode, you can shoot the penguins for 5 or 10 points each. However, in the last round the penguins slide down the iceberg and jump into the air. Shoot the penguins in the air for 50 points each.