You see a puzzle “shape” made up of empty (blank) spots.
At the bottom (or somewhere), there are colorful blocks (pieces), each made of line-segments or shapes.
You drag a block using your finger (touch screen) or with mouse (click & drag)
You place it into the puzzle shape so that it fits — you want to fill all blank spots, leaving no gaps.
There is no time limit, and there’s no losing condition — you just progress by completing levels.