Bring the number down to zero! Each level contains a white square with a number on it, and red blocks with numbers. Click on a red block and drag your mouse to move it into the white square, then release. The number on the white square will be reduced by the number on the red block. You need to place all the red blocks in the square to bring the number down to zero.

You can also place multiple red blocks in one white square to bring the number down to zero.

Some white squares will be broken up. If you have a large red block, you can place it on multiple white squares to reduce more numbers at once!