Chords are three or more notes played together (two notes played together is called an interval).
Lets take the C major chord as an example.
The notes in the C major scale are;
C D E F G A B C lets give each note in the scale a number.
1 2 3 4 5 6 7 8
All major chords contain 3 notes (often with a guitar chord you are playing all six strings when you strum a chord but that just means some / or all of the 3 notes in that chord are being played on more than one string).
If you take the 1, 3 & 5 notes from the major scale then you will have the three notes needed for the C major chord ir. C E G.
NOW HERE IS THE IMPORTANT BIT. You can use the same idea to work out any major chord.
For example.
The A major scale is
A B C
D E F G A
1 2 3 4 5 6 7 8
So if we take the 1,3 & 5 notes we get the three notes needed for the A major chord (A C E).
