The strings of the guitar are numbered 1 through 6, highest sounding to lowest sounding
In the standard tuning from the guitar, the pitch of the string is E, A, D, G, B, and C, going from string 6 through to string 1.
String 1 is two octaves higher in pitch than string 6.
The musical distances between the strings are ascending perfect 4ths (4 note names, 5 semi-tones), with the exception of the distance from the G to the B, which is a major 3 (3 note names, 4 semi-tones).
This irregularity in standard tuning means that patterns of notes can not be moved from string 3 to string 2, or vice-versa, without making a one fret change in the pattern. When moving a note pattern from string 3 (G) to string 2 (B), the notes must all be moved up the neck one fret. When moving a note pattern from string 2 (B) to string 3 (G), the notes must all be moved down the neck one fret.
The significance of the irregularity will become clearer as we get into examples of scale and chord transposition by moving across the neck.