Commits are snapshots of a tree. They have a list of ancestors (usually, but not always, just one). Tags are named pointers to a commit that don't change. Branches are named pointers to a commit that do change. The index is a tiny proto-commit still in progress that you "add" to before committing.
There. That's git. Want to know more? Don't read the guide, just google "how to I switch to a specific git commit without affecting my tree?", or "how do I commit only some of my changed files?", or "how to I copy this commit from another place into my current tree?".
The base abstractions are minimalist and easy. The things you want to do with them are elaborate and complicated. Learn the former, google the latter. Don't read guides.
Because the C and PL/SQL people are on CVS, I can fix this with vi on the ,v archive.
First on TFS repositories, and now with git grep I can easily find exposed passwords for many things. But it's just SQL Server!
We will never be able to use git responsibly, so I will peruse this guide with academic interest.
Don't even get me started on secrecy management.
I am looking forward to retirement!