Major chords are constructed with the 1st, 3rd, and 5th notes of the Major scale.
Minor chords are constructed with the 1st, b3rd, and 5th notes of the Major scale. "b3" means that the third note of the scale is lowered by one half step.
Let's look at the chord tones of some common Major and Minor chord shapes below.
A Major
This common A Major chord shape is constructed of 1 (R for root), 3, and 5.