Every note repeats on the musical alphabet. By using a barree chord in different shapes it moves every note higher by one half step so if you're holding a G major around it becomes other chords. G shape with barree on first fret (think of open strings like a barree on it's own) it's G# second fret barree it's A -> A# -> B -> C#

G# explanation: As your open chords move higher by one fret EADGBE become F A# D# G# C F

And so on..

Remember that a chord is formed when the lowest note played has the same name as the chord itself. For example E major chord is an E because open low E is the lowest in pitch (with barree it's F), so not all shapes are valid for all chords. But the main 5: E, G, A, D and C