In any key it is possible to build chords on each note of a scale. This means that for every major scale there are seven possible chords which can be used for creating guitar parts and harmonising melodies. These seven chords are called scale tone chords. It is common practice to describe all the chords within a key with Roman numerals. Here are the seven scale tone triads (three note chords) in the key of C major.
Once you know the notes for any of these chords, you can use any fingering you know to play them. This may involve re-arranging the order of the notes or doubling some of them, but as long as the chord shape you are playing contains only the three note names of that particular chord, you are still playing the right chord. This common progression in the key of C could be described as 1 3 4 5 3 6 2 5.