We need to start adding files for git to start tracking, the command to do this is:

git add file_name.txt

From this point git will track whether this file has been changed or deleted. This command however is a little inconvenient if you need to add alot of files, WordPress itself is comprised of a few thousand files!

Luckily this is easy to accommodate for, instead of using file_name.txt, you simply type .. This will recursively add files and folders from your current folder down, meaning that it wont add anything above your current folder.
When you add files, make it a reflex to also do

git status

so you can check everything went to plan.