Una corda pedal
The typical modern grand piano has three foot pedals. In contrast to an organ, these pedals aren’t used to play any notes. They are used to adjust the way the piano plays. When the piano was first invented, some of these pedals were created as “stops”, which are little levers you would pull with your hand. A pianist typically needs both hands, so they were later moved to knee levers during Mozart’s time. Finally, they evolved into the foot pedals we know of today.
It’s important to understand not only when to use the pedals, but what they actually physically do to the piano. Once you understand how the pedals affect the sound of the piano, understanding when to use them will come more naturally.