I think you should start by learning your major SCALES. Once you learn those, then major chords can be found easily. For example, a major chord (triad) is the 1st, 3rd, and 5th notes in the major scale, and a major 7th chord is the 1st, 3rd, 5th, and 7th notes in the major scale. Does that make sense?
Also, there is a pttern to all major scales, no matter what key you are in, and that deals with note spacing. To go from one note to the next higher note is an interval called going a half step. For example, going from B to C, or going from F to F#. So, going up two half steps is called moving up a whole step. For example, going from B to C# and F to G. Does that make sense?
Now, the pattern for major scales in any key goes like this:
- start at the note in which key you are in (tonic note).
- then go, whole step, whole step, half step, whole step, whole step, whole step, half step. (W-W-H-W-W-W-H)
- you should end on the same note you began with but at one octave higher (like going from middle C to the next higher C).
- all the notes you have played with those step intervals comprise your major scale.
Does this make sense?
Example: Key of C
Major Scale: C - D - E - F - G - A - B - C
Your starting note is C (tonic) because that is the key of the scale. D is a whole step ( 2 half steps) away from C. E is a whole step up from D. F, however, is only a half step up from E. And so on.
Example: Key of A
Major Scale: A - B - C# - D - E - F# - G# - A
The principle applies to all major scales in all key keys.
Then to find out what the Cmajor chord is, you take the C major scales, and play the 1-3-5 (C-E-G). To play the A major chord, you do the same (A-C#-E). I hope this makes sense and help you. God Bless!