1. Once you open the app, you'll be taken to the main menu. Here, you can choose to start a new game, continue playing an existing game, or change the game settings.

2. To start a new game, tap on the "New Game" button. You'll then be taken to the game screen.

3. The goal of Classic Tetris is to stack falling blocks in such a way that they create complete rows without any gaps. When a row is complete, it will disappear and you'll earn points.

4. To move the falling blocks, use the virtual joystick located in the bottom left corner of the screen. To rotate the blocks, tap on the screen. To drop the blocks faster, swipe downwards on the screen.

5. As you play, the blocks will fall faster and faster, making it more challenging to create complete rows. If the blocks reach the top of the screen, the game is over.

6. To pause the game, tap on the "Pause" button. Here, you can also adjust the game settings or quit the game.

7. To save your high score, make sure you're logged in to the app with your account. Your high score will automatically be saved and displayed on the leaderboards.