Git's guts: Branches, HEAD, and fast-forwards

Lets get some learning done. There are a few questions that keep cropping up when I introduce people to Git, so I thought I'd post some answers as a mini-series of blog posts. I'll cover some fundamentals, while trying not to retread too much ground that the fantastic Git community book already covers so well. Instead I'm going to talk about things that should help you understand what you and Git are doing day-to-day.