Open A tuning is the same as open G tuning only a whole step higher, the same chord shapes work in both tunings (only a whole step higher).

On an electric guitar with very thin strings and low action open A makes it easier to play with a slide or bottleneck as the strings are tuned higher than in open G.

Tip for beginners... Most blues tunes and many rock tunes revolve around three chords, the three basic chords are the I, IV and V chords which can also be called tonic, subdominant and dominant. In the key of A these are A, D and E. The I chord is either on the 12th fret or open strings, the IV chord is on the 5th fret and the V chord is on the 7th fret.