It seems that everyone is familiar with the right damper pedal, but I am often asked what the other two for.
Each pedal on the piano has it's own unique purpose for enhancing the dynamic quality of a piece. Some upright pianos only have two pedals, the soft and the damper. Most people are familiar with the damper or sustain pedal, located on the right of the keyboard. When in use, this pedal collects and sustains each note that is played, giving the player advantages in many musical situations.
The soft, or muffler pedal is located on the far left of the piano. As its name suggests this pedal softens the sound of the piano. This gives the pianist the ability to play softer musical passages with much more expression.
This misunderstood pedal in the middle is the Sostenuto. The sostenuto pedal allows the pianist to sustain certain notes, while other notes remain unaffected. It is used by playing the underlying sustaining notes, then depressing the pedal. The selected notes will resonate until the pedal is released, while new notes will be unaffected. This way, sustained notes can be heard alongside notes played with a staccato effect.