Vibrato is slight, rapid, variations in pitch. Your fretting hand can achieve this by rolling your finger tip back and forth between the frets. A common misuse of language (damned marketeers!) has resulted in the 'whammy bar' being referred to as a tremolo when it is actually an extreme vibrato device. Tremolo (tremolando) actually refers to fluctuations in the loudness of a note.

Harmonics are whole-number multiples of a frequency. The fundamental tone is taken to be the first harmonic. The 2nd harmonic occurs at twice the frequency of the fundamental; the 3rd harmonic occurs at three times the frequency of the fundamental, etc.