At level one, your Sim only starts practicing the chosen instrument. At level two, the Sim can research the instrument and appreciate music played on it when listening to the stereo. At levels three to seven-, your Sim learns how to play more musical genres on the instrument. At level eight, you unlock the songwriting option and can play classical songs. At level nine, you get to license your songs and get royalty payments. When you reach the maximal skill level, you can become a mentor.