A couple of general rules (meaning that they aren't always true, but for these purposes will work for you)
You will hear a lot of folks tell you that a minor chord is a "major with a flattened third" and an augmented chord is a "sharpened fifth" but I've found that to be a whole lot of information to keep track of.
So I remember it this way.
All of your chords are derived from scales. They will generally be the first, third, and fifth notes. Chords with a '7' in them will add in the 7th note of the scale as well.
As an example, lets look at C major.
The scale is C D E F G A B
As a chord, that's C E G - the 1st, 3rd, and 5th notes.
A minor -
Scale is A B C D E F G
Chord is A C E, again, the 1st, 3rd, and 5th.
Scales is where it's at. They're pretty much the foundation of everything, including the chord structures.
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