Remember that when moving FORWARD on the fretboard, the sound of the notes gets higher and when BACKWARD, the sound gets deeper or lower. So when you play the strings, you are playing the alphabet notes, at the same time when you move up and down the frets, you are playing the numerical frets.

Example: string A is played on fret 0, string B is played on fret 2, String C is played on fret 3, D is played on fret 5, e on fret 7, F on fret 8 and G on fret 10.There are 4 frets which have no alphabet strings played, 1, 4, 6, and 9.

If the distance between two frets is a half step, then when skipping a whole fret means that this is a WHOLE STEP. So in jamorama which means, string B/C and E/F are the only ones which are half steps, the rest are whole steps.