The open strings
In standard tuning, the strings from thick to thin are: E, A, D, G, B and E. A handy mnemonic: 'Eddie Ate Dynamite, Good Bye Eddie'.
The thickest and thinnest strings are both an E, two octaves apart.
Every fret is a semitone
Each fret raises the note by a semitone. The twelve notes are: C, C♯/D♭, D, D♯/E♭, E, F, F♯/G♭, G, G♯/A♭, A, A♯/B♭, B.
Note: there's only a semitone between E and F, and between B and C. So there's no sharp or flat note between them.
Fret 12: it starts all over again
At fret 12 you play the same note as the open string, but an octave higher. After that, the pattern repeats. The dots at fret 12 help you find your way back.
Start by learning the notes on the low E and A strings: that's where the root notes of most chord shapes live.
Practice tip
Pick one note each day, say G, and find it on all six strings. Say the name out loud as you play it. The fretboard map shows you exactly where they are.
Read also

Major and minor
Why one key sounds cheerful and the other darker.

Pentatonic Scale Guitar
Five notes that let you start soloing straight away.

Soloing over the 12-bar blues
The most famous chord progression in the blues, and how to solo over it.

Pentatonic licks that always work
Four classic licks in A minor, with tab.

