What he said. Haven't you guys learned the basic chords:

e |-0--
B |-1--
G |-2--
D |-2--
A |-0--
E |----

is A minor and

e |-0--
B |-2--
G |-2--
D |-2--
A |-0--
E |----

is A major

I'm basically just reposting what davie_gray said.