This article about branching in Git is probably the one that helped me understand it the best. It does a really good job of illustrating (literally) the concepts of using branches in git to manage your stable, development, and experimental code, without losing your sanity.
A successful Git branching model » nvie.com
Original Article: A successful Git branching model » nvie.com Dougal Campbell's geek ramblings - WordPress, web development, and world domination.