In grappling, one will inevitably find themselves with someone in their guard. The jiu-jitsu guard is one of the most versatile positions because of its potential for sweeps and submissions. The control that it offers is sometimes preferred to having a top position by BJJ (Brazilian Jiu-Jitsu) guys. These videos teach some slick techniques.
Closed Guard BJJ Techniques
Two BJJ Sweeps from the guard
Taking The Back From the Guard Sleeve Control With GI