git init

• Tutorial
• Cheatsheet
• Resources

Resources

Intermediate

• How to write a Git Commit Message
• Git immersion: A more in depth (and long) tutorial explaining: basics, branching, remote repositories, git internals, aliases, and more.
• Justin Hileman's chart to solve a git mess
• Github's Git Cheat Sheet

Advanced

• Learn Git Branching: Visual explanation of Git Commit Trees. Includes a really good explanation of the differences between merge & rebase.
• Scott Chacon explaining how Git works internally