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:
Creating Pentatonic Scales
The great use of pentatonic scales comes from their versatility; they can be played over more changes and keys as they have less notes between the octaves, meaning less notes to clash with those that are in the chords being played over.