The main idea in Shifter is to collect three or more colored squares so that they explode vertically or horizontally. This way, more colored blocks will appear so you get more points for making them explode and can then level up.
This puzzle will add special blocks as you advance through the screens, like a block that changes color and can be used wherever it's most useful.
If the time runs out before you can merge several blocks of the same color, you lose. Shifter saves your high score on a board, so you can try to beat your own scores or those of the computer's other users.