1. Place your left thumb on the thumb rest.
2. Place your left index finger on the top key.
3. Place your left middle finger on the A key.
4. Place your left ring finger on the key below the A key.
5. Place your left pinky finger on the side key.
6. Blow into the mouthpiece while pressing down on the A key with your left middle finger.
As you blow, make sure to keep your fingers down firmly on the keys and your lips tightly sealed around the mouthpiece. You may need to practice a little to get the proper embouchure and finger placement to produce a clear, consistent A note.