The IDPA Classifier is a standardized 90 shot course of fire that is required for IDPA members to be classified - Master, Expert, Sharpshooter, Marksman, Novice - in sanctioned competiton. It is completely described in the rule book and is on the IDPA.com site.
It is not real popular among shooters who want novelty, excitement, and entertainment, so it is not offered very often. About all you can do is ask the local club(s) to notify you the next time it is offered.
Around here, it is often done as an add-on before or after a regular match, for those who need a classification. Ask, there is no reason not to get together with an SO and have him run you through the Classifier on an off day.