Major chords/triads are made using the major scale for the particular note in question.
C major chord will need the C major scale.
Then we use the 1st,3rd and 5th notes from that scale and play them together to make the major chord.
The C major scale would be:
C D E F G A B C
Then take the 1st, 3rd and 5th notes
C, E and G and play them together
The Caged System Workout