A two finger chord just means you’re using two fingers on your left hand. Two chords usually involve hitting some open strings as well.
Three finger chords mean you’re using three fingers on your left hand to make the chord. These are helpful because you can move them around the neck easier because you aren’t relying on open strings. Not all the chords sound as good with open strings so that’s where 3 finger chords can be handy.
All the chords have a 2 finger version and a 3 finger version and sometimes even 4 fingers. Once you learn the different chords you can decide which version you’d like to use.
If you have any more questions let me know.