Use arrow keys: left/right to move, up to rotate, down for soft drop, space for hard drop. On mobile, use the on-screen buttons. Clear lines by filling complete rows.
Single line = 100 points, double = 300, triple = 500, Tetris (4 lines) = 800. Points are multiplied by your current level. Speed increases every 10 lines.
The transparent outline at the bottom shows where your piece will land if you drop it. This helps you plan placements more accurately.