A musician class should have functions which any musician will have, such as:
getInstrument() to get the type of instrument the musician is current playing.
setInstrument() to set the musician's instrument to a particular instrument, such as a guitar.
sing() to get the musician to sing lyrics (probably specified in a string parameter), and probably synchronised with the music he's playing (don't know how you would implement this, it would probably take a lot of work).
Since there are different types of musicians (e.g. guitarists, bass players, drummers, etc.), you should probably make the musician class generic enough to derive specific musician classes off of. Also, since every musician is a person with his/her's own personality, you could probably derive the musician class off a person class which provides functions for the person talking, walking, etc..