There are often three pedals.
The right pedal is known as the sustain pedal and does just that, sustains a note, often referred to as the pedal.
It can be used in three different ways, BEFORE the sound(key stroke) called ANTICIPATED PEDALLING, at the same time as the key stroke or AFTER known as SYNCOPATED PEDALLING.
Of the other two only one is normally found on an UPRIGHT PIANO the extra normally is only found on GRAND PIANO's.
The left is the UNA CORDA pedal which moves the hammers within the piano in different ways depending on whether it is a GRAND PIANO in which the hammers are moved sideways so that every 3rd string is untouched out of every three played.
UNA CORDA is ITALIAN for ONE STRING.
In an upright the left pedal moves the whole set of hammers closer to the strings so that they have less effect, known as the SOFT PEDAL.
The centre one(if fitted) SOSTENUTO PEDAL, which allows the pianist to make a selection of the notes he wishes to sustain in advance .
tabetha