Open shape
x02210
Am is the A minor chord. Its notes are A, C and E. The lowered third gives this triad its darker color.
x02210
577555
Numbers show frets from the low E string to the high e string; x means don't play that string.
Am is the ii chord in G major, the iii chord in F major and the vi chord in C major. That makes it a natural fit in songs written in those keys.
Every A, C and E on the first 12 frets. The filled dots are the root, A. Build your own shape from any nearby group.
Other A chords
Other minor chords