Here is a number of links to resources I found useful.

• There is a great (and free!) book available called Pro Git. At the very least you should read the chapters 2 (basic operation) and 3 (branching and merging). Although I had worked for almost a year with Git before coming across this book, it greatly improved my understanding. I especially liked the great visuals that make it pretty easy to grasp things quickly. An absolute must-read!
• Git tutorial: A nice reference for quickly looking up things
• Setting up Apache for Git push via HTTP(S)
• Installing Git from source on Debian
• Setting up SourceGear DiffMerge with Git
• Git casts
• Git community book