The object of Block Boxer is to destroy the enemy blocks. In order to do so, use the arrow keys to move your block so that your block either lands on top of them or rams them at high speeds (but be careful, if your block isn't higher than the enemy, you might be the one getting squashed!).
In the beginning, each enemy has two lives. However, as you progress through the levels, the enemies will get more difficult, increasing speed, aggressiveness, and their number of lives. There are several achievements that can be unlocked for killing the enemies.