This is a puzzle from the old C64 Impossible Mission game.
The idea is to combine the 36 tiles in sets of 4, such that each set
of 4 makes a solid block. Clicking on the tiles on the left toggles
them. A tile can't be turned on if it overlaps with any existing on
tiles. The lone rectangle on the right is the combination of all
the on tiles. Clicking on that is an easy way to turn all tiles off.

When 4 tiles combine to make a solid block, they vanish. The goal is
to get rid of all the tiles. There is no score or timer. Just do it
for the intellectual exercise.