An octave is the range of eight notes of a major scale. The first note and the last note of a major scale always have the same name. In the C major scale the distance from the lowest C to the C note above it is one octave (eight notes).
Practice playing this scale ascending and descending as a warm up before practice.
Many heavy metal bass runs and licks are based upon scales.
The bass run in the example below uses notes from the C major scale.
The distance of two frets is called a tone.
The distance of one fret is called a semi-tone.
The notes Band C are separated by one semi-tone (1 fret).
The notes E and F are separated by one semi-tone (1 fret).
All other notes are separated by one tone (2 frets).