Click on the orange play button and then on the first level to begin. Your goal is to destroy all the pigs using the least amount of crazy birds. To do so, use your left mouse button or your finger to pull back the bird on the sling, taking into consideration angle and strength, and hurl it at the pigs and their buildings to bring it all crashing down! As you advance in the stages, you will get all sorts of new birds, each with their own special attack.
Tip: You can also take out pigs by collapsing large parts of buildings on them!