Grow and shrink the squares to clear them by forming chains of 3 or more of the same size and color.

You can build longer chains by rapidly clicking on adjacent squares. Create combos (Chain reactions) and get bonus score.

If all 6 blocks in a row are same- all blocks on screen of that color are destroyed . This also gives you magic erasers, that you can use to remove single squares. 

Right-Click or hold down Control to Quick-remove squares.