I have a question: About classical music, What's the difference in a Counterpoint, a Canon and a Fuge?

Counterpoint = music consisting of two or more melodic lines sounding simultaniously.
Canon = a device of counterpoint, where a certain melody is repeated in its entirety in one or more voices throughout the entire peice. It's the strictest of the imitative counterpoints.
Fugue = A polyphonic composition based on a theme which is stated at the beginining in one voice alone, then imitated in close sucession by another voice or other voices, and then reappears in various places in various voices.