Instructions
Use the "A" and "B" buttons on your gaming console's controller if you're paying "Tetris" on a console like the Nintendo Entertainment System or the Nintendo Wii. Using the "A" button will rotate the selected block to the left while using the "B" button will rotate the selected block to the right.
Press the "Up" arrow key on your keyboard (if you're playing a version of "Tetris" on your computer). On most computer versions of Tetris, the "Up" arrow button is the only one responsible for rotating the block. The block will only rotate to the left or the right, not in either direction. Keep this in mind while playing.
Tap the screen (if you're playing "Tetris" on a device with a touch screen interface like the iPod Touch). On mobile versions of the game, tapping the screen is typically responsible for the rotation of the blocks. It acts the same way the "Up" arrow would on a computer and only rotates the block in one direction as opposed to two.