The half step spans 1 fret. There are 12 half steps in the chromatic system. Two half steps equal a whole step . The note you hear is one octave higher than the fretted note in that position .
Harmonics are possible over much of the neck.
The exotic harmonic minor scale has many uses in jazz. Go to a lesson on the Harmonic Minor Scale here. Adding two or more notes together. In jazz the word reharmonize is often used to indicate substituting the original chords in a song with others. See substitution here .