Form squares or rectangles as big as possible to eliminate all the blocks that are within. It doesn't matter how far apart the imaginary corners that form them are, just click on them to form the square or rectangle. Overcome the challenge in each different level.
The best way to rack your brains is to spend some time every day trying to solve puzzles. These games will make those moments great fun.
We've all played on many an occasion the typical video game about shooting balls to join 3 or more identical ones...