Major Chords

We've had a look at intervals ('diads') and now we'll look at triads.
The notes at positions 1, 3 and 5 are very important to making chords.
OK. Take the root, 3rd and 5th of any scale, and you've got the major chord.
So D major would be:

1	3	5
D	F#	A

because the scale of D is:

1	2	3	4	5	6	7	8
D	E	F#	G	A	B	C#	D

You can take the notes in any order, anywhere on the fretboard and they'll sound a D major of some description.
Some sound better than others. Find the ones you like and / or are easiest to play.
If you want to know the technical difference between them, have a look at inversions otherwise carry on to
a list of major chords , some more chord theory, or have a look at Power Chords which are
nifty two note chords that rock guitarists use but they work well on longer length mandolas and bouzoukis as well.