The game is played by clicking on groups of the same color to eliminate them from play. Of course, the larger the group the more points awarded. But doing so also clears valuable space to fit more blocks, a new batch of which will fall into play with about every fourth click. Only by clearing very large groups (16+ blocks) can you earn a free click.
There is no "beating" this game that I could tell, the game ends when the play field fills up completely with blocks. There is a nice indicator on the bottom center of the game window that will always tell you how many blocks are in the color group under the mouse cursor. Use it to find the largest of groups available. Three Degrees is a very simple game to pick-up and play, a nice variation on a classic, and one that you will likely find yourself playing again and again.