As you learned in section 1, a semitone is the smallest distance between two notes used in western music. On the guitar, notes which are a semitone apart are one fret apart, (e.g. the note C on the 3rd fret 5th string is one semitone above the note B at the second fret). Notes which are a tone (two semitones) apart, are two frets apart. An example of this would be the notes F and G on the sixth string or the first string, or the notes G (open) and A (2nd fret) on the third string. Visualizing these distances can help you memorize scales more easily.