The primary motion of a conductor represents the time signature of the piece being played: there are specific patterns used for different time signatures. The rest of his motion is specific direction to musicians (louder/softer, etc.)

Looks like someone posted a good YouTube on this, but also check your local library for DVDs (and streaming) of productions by The Teaching Company.

They cover just about everything, from Introductory Sewing to Quantum Electrodynamics.

I've listened to some amazing Music History and Music Theory stuff, so they may have something on conducting.