How Do Primaries and Caucuses Work?

I had a general idea how the non-incumbent party elects its representative to run against the sitting president, but I was still hazy on the nuances of the process. This video laid all the details bare in an easy-to-understand, entertaining fashion: http://thereformedmind.wordpress.com/2012/01/12/how-does-the-presidential-primary-system-work/