Blow up as many blocks as possible in as little time as possible! Each bomb costs money, so try to place them so, that you reach a maximum effect. As soon as you've earned 1000 dollar, you can pass on to the next level. So you don't necessarily have to make all the blocks disappear. The bigger the blocks you make disappear, the more money they earn you.
Click there, where you want to put a bomb and press the spacebar to make the bomb explode.