You only use these three notes in the chord. Now for the easiest way to find a major chord look at the shape made on the A, D and G strings. G--0 D--2 A--3. This is very useful device for chord formation. Find this shape anywhere as long as the root note is on either the E or the A string to find a major chord. The bottom note is the C, the middle note is the E and the top note is the G. If you wanted to find a D chord you can use the same method. Just find a D and off you go D--7 A--9 E--10 Work out the notes and you've got D, F# and A, the three notes of a D major. And if you were to look at what you would know as a D major chord.
E--0 E B--1 C G--0 G D--2 E A--3 C E--X *
Look and you've got a D, an A another D and an F# - Perfect! It's really easy once you strip it down to the bare bones of maths - just remember the shape of the fourth finger on the root note you want to find the chord of, third finger one string up and one fret down, and first finger another string up and two frets down. All you have to do is work out the notes. Minor Chords. Now you've learnt how to make a major chord, it can be really easy to learn a minor chord. If you take what you had of the root note, four semitones up and then another three semitones up for a major chord, a minor chord is almost exactly the same but instead you take the root note, go three semitones up, and then go four semitones up from that (still seven semitones from the root note.) So if you take an A minor, you take A, go up three semitones to get a C, and then another four up to get an E. Let's have a look at the chord
E--2 F# B--3 D G--2 A D--0 D A--X * E--X *
There, easy as chips. But to make it even easier there is another basic chord to shape to get the notes. It's just like the last one but instead use your second finger where you would use your first, so where you did have D--2 A--4 E--5 Instead use D--2 A--3 E--5 And guess what - it's almost exactly the same! So if you want to find another chord, let's say E minor - find and E and away you go D--9 A--10 E--12 And what are those notes well you've got the E you started on a G and a B. And what are the notes of an E minor
E--0 E B--1 C G--2 A D--2 E A--0 A E--X *
So you now have a really simple way to make minor and major chords. Part 2 will be coming shortly to show 7thh chords, Major 7th chords and minor 7th chords, Sus2 and Sus 4 chords and possibly others if there are requests in the comments. * I'll briefly explain why you don't play a note on some strings. I'll give the example of a C which was the first asterix to come up. the reason you don't play a G on the E string is in the simplest terms possible so you don't drown out the C. You always have to keep the C dominant, but the only note you can reach would be a G. If your forming a major chord try and make sure that at least 40% of the notes are your root note.
E--0 E B--0 B G--0 G D--2 E A--2 A E--0 E