The goal
Place geometric pieces on the board, clear complete rows and columns, and keep enough open space for the remaining tray pieces.
Place a piece
Drag a shape from the tray onto a legal group of empty cells. The complete shape must fit; occupied or out-of-bounds cells reject the placement.
Clear lines and refresh the tray
A fully occupied row or column clears after placement. One move can complete more than one line. After all three tray pieces are used, GridD deals three new shapes.
Keep the run alive
The run ends when none of the available tray pieces can fit. Check all three pieces before committing a large shape, preserve flexible open areas, and look for placements that prepare more than one line.