How to Find Notes
The easiest way to break down finding notes on the guitar is to simply learn the dotted notes on the lowest two strings (E and A), and then learn the basic shapes to help you find all the same notes.
The dots on the Low E and A strings are the first thing to learn. Each fret moves you one note higher or lower. The notes on any string are determined by the open string, that is, what note the string is when you don't fret it (e.g the Low E string is an E note when played open, therefore the first fret of the Low E is an F note). The order of notes in music are as follows:
A, A#/Bb, B, C, C#/Db, D, D#/Eb, E, F, F#/Gb, G, G#/Ab, A etc..
Remember: Sharp (#) = UP Flat (b) = DOWN
Blue Cats Eat Fish = No Accidentals between B and C, or E and F
From each note on the Low E and A strings, if you just go up two strings and up two frets, you will find the exact same note an octave higher. This can also be done in reverse (if you're on the D or G string, go down two strings and back two frets and you'll find the same note an octave lower). Because the B string is tuned slightly different, this shape just increases by one fret when you use the B string. All that is shown here:
The 5 Root Shapes
Across the fretboard there are set shapes between one note and the next. On the diagram below are outlined the 5 basic shapes we can break these down into. These shapes apply no matter the starting note, and always follow eachother in the way displayed here.
Creating Pentatonic Scales
In all of these positions we can create pentatonic shapes to riff and solo with. Learn each position on its own before adding the next to avoid confusing the shapes, then make some riffs!
Seventh (7th) Chords
The basic idea of creating 7th chords comes from adding one more 3rd interval on top of your existing major or minor triad. The most common 7th chords and their formulas are as follows:
Major 7: 1 3 5 7
Minor 7: 1 b3 5 b7
Dominant 7: 1 3 5 b7
Harmonising 7th Chords
7th chords are relatively easy to fit into a diatonic key because for the most part they can be used instead of standard major and minor chords in the key. The major 7th chord scale is as follows:
1 - Maj7
2 - min7
3 - min7
4 - Maj7
5 - Dom7
6 - min7
7 - m7b5 (still to be considered dimished harmony)
Relative theory also applies to these chord scales, and so any minor key can be considered as the relative major chords beginning on the 6th degree:
1 - min7
2 - m7b5
b3 - Maj7
4 - min7
5 - min7
b6 - Maj7
b7 - Dom7