Notes on the 6th string

The best way to memorize the natural notes on any string is to start out just playing (and naming) a few notes and progressively add 1 note at a time. (e.g. play E F G E G F G A F A B F G B C etc...) If you do this a little each day you can learn the note on the neck quickly. Also notice where the notes are in relation to the fret markers (usually at the frets 3, 5, 7, 9 and 12 also 15, 17, 19, 21). At the 12th fret the note is the same as the open string only sounds higher, this is called an octave. Beyond the 12th fret the names of the notes just repeat. The higher fret markers are equivalent to the lower ones just and octave higher (15=3, 17=5, 19=7, 21=9 )

Notes on the 5th string

Go through the same process as the 6th string. After learning the natural notes on the 5th and 6th string do the same on the 4th, 3rd, and 2nd. The 1st string is the same as the 6th string.

Sharps and Flats

A sharp (#) raises a natural note by a half step (1 fret).

A flat (b) lowers the natural note by a half step.

So between each set of notes ( except between E-F and B-C ) there will be a sharp/flat note. (e.g. the note between F and G is F# or Gb, they are the exact same note just with a different name)

Notes that sound the same but have a different name are called enharmonic.

Another great way to help yourself learn the names of the notes on the neck is to use octave shapes to find the names of the notes on the less familiar strings.

page 1, names of notes on the neck