Make sure you've saved the script. Now, click on the git tab in RStudio. You'll notice that there's only one file listed -- our script -- since that's the only file that's changed.
Click on the staged box to stage our change. Now click on Diff to give a summary of what's changed. Lines that have been added are green. Lines that have been removed are red.
From git's point of view, a modification to a line is actually two operations - The removal of the original line followed by the creation of the new line.
Add a commit message and click on commit
In the git tab of RStudio, click on diff and then History. You'll see that you can look through every commit you've ever made. This can be extremely useful for finding bugs or looking back to how your model looked a few months ago.
It's not possible to revert back to a previous commit using the RStudio interface. For that, you need to learn some command-line git which is beyond the scope of this session.