Being able to construct chords, to know what notes make up a chord and why, is one of the most helpful fundamental pieces of music theory you can learn. Let’s go through some basics together.
Major chords are made up of the 1st, 3rd, and 5th notes of the Major scale. C Major, for example, is made up of C, E, and G notes.
Minor chords are made up of the 1st, flat 3rd, and 5th notes of the Major scale. C Minor, for example, is made up of C, Eb, and G notes.
We can see here that there is just one small difference between a Major and Minor chord, the flat 3rd (minor third) note instead of the 3rd (major third).
Below are some important chords to memorize. On the left will be the chord name, and on the right will be the notes of the major scale that make up that chord.
Major = 1 3 5
Minor = 1 b3 5
Diminished (dim) = 1 b3 b5
2 (sometimes called "sus2") = 1 2 5
sus (sometimes called "sus4") = 1 4 5
6 = 1 3 5 6