(I have been playing guitar about 2 weeks now) My buddy showed me a A minor chord on guitar and played it with a A(5th string) E (4th string) a(3rd string) c (2nd string) and open e (1st string) But i thought the formula for a A minor chord was 1 flat 3 5, wouldn't that be A c flat) e?! Im so confused, please help!
in the key of A Major, C is sharped, so to make it a minor chord you flat the C to make it C natural.

A Major: A B C# D E F# G#
A minor chord: 1 b3 5 = A C E
When talking about chord structure you use the major scale of the root note to build the chords, yeah.
Scale of A minor is A B C D E F G A. First is A, third is C, fifth is E. You can also find the chord by flattening the third of the major scale, which makes that third minor.