Smart Controls and Swipe Controls are two different ways to control the game. Go to the Settings tab to choose between them.
When using Smart Controls, touch the screen to see the ghost piece. Drag around to find the best fit for the Tetrimino, and release to drop it.
When using Swipe Controls, tap the left or right side of the screen to rotate the falling Tetrimino. Drag left or right to move it. Flick down to Hard Drop. Flick up to Hold.