Most modern acoustic pianos tend to have three pedals. The right hand one is the damper (sustain) pedal, the left one is the soft (una corda) pedal and the middle one is the sostenuto pedal.
Very simply the damper pedal sustains all keys played for the time the pedal is depressed. When the soft pedal is depressed (on an acoustic piano) the hammer which normal strikes three strings for each note, only strikes one of them which makes the sound softer and also alters the tone somewhat. The sostenuto pedal enables the pianist to sustain selected keys, while other keys remain unaffected. On digital pianos often, the middle (sostenuto) pedal can be assignable.
When purchasing most portable keyboards, pedals are rarely included, but at the very least you would need a sustain pedal. Single, double and triple pedals for these are widely available.
Some digital keyboards also support ‘half pedaling’, where the sustain level can be varied according to how much the pedal is depressed.
In addition to the sustain pedal you may also find a swell pedal useful if you want to use organ sounds. This just simply increases and decreases the volume and is a fixture on all organs.
If you want to play bass with your feet, you may want to add a pedal board (with swell pedal included). These are primarily used for organ music. The one shown below is a Nord.