Eventually, we will dress up this post with graphics but we wanted to get this links all put in one place. Here they are:
Nice, concise overview of the Classifier Stages and Strings with a good diagram:
http://www.cbshooters.com/idpa/files/IDPA_Classifier_Match_Scoring_and_Layout.pdf
IDPA's official description of Stage 1:
http://www.idpa.com/compete/stagedetails/39
IDPA's official description of Stage 2:
http://www.idpa.com/compete/stagedetails/40
IDPA's official description of Stage 3:
http://www.idpa.com/compete/stagedetails/41
Great Advice from the Dallas, Texas, area IDPA.
http://www.ccidpa.org/classifier-tips.html