Now, let's talk about the pedal in electronic pianos. The main purpose of this pedal is to imitate the sustain pedal (the right pedal) of the acoustic piano.
However, there are some electric pedals that can imitate the two others pedals. First, you should understand the function of the other pedals (because it changes from piano to piano). And then, you should see if these functions exist in the electric pedal that you purchase. I advise you to check if the electric pedal is compatible with your electric piano..
To summarize, the electric pedal is mostly used for the sound of the sustain pedal which makes the sound longer, fuller and with echo. The functions of the other pedals are less used and I wouldn't put much effort in finding these kinds of pedals.
I hope that I have helped you, Ido from www.piano-play-it.com