This is a good place to start to wrap your head around simple version control techniques with git. (The cheat sheet provided is also worth the download)
This tutorial is is pretty extensive and includes integration with RStudio. (Recommended by Alex and John)
One of the more comprehensive guides I found. It starts from the command line and then links you to a GitHub account to make collaborative changes. We can then try making changes on each other's repo on GitHub for the next meeting.
Key features:
Starts you from scratch
Contains efficient workflows for each section
Has short exercises at the end of each lesson to test understanding
Easy to read language
JH: Here is a git tutorial I made. Maybe this will be helpful to those getting started using git from either Rstudio or via the command line.