"The most basic usage is: git reset useful_func.clj This will replace the useful_func.clj in the current working directory with the last committed version in the repository HEAD."
Not a good start. What it actually does is reset the path "useful_func.clj" in the index (AKA staging area) to the HEAD state. It doesn't touch the working directory.
Git guidance should almost always start with a brief introduction to the concepts you believe the audience doesn't know or fully understand. To begin with reset and not properly explain the index will just end up being confusing, especially with brief references to hard, soft and mixed resets later on!
So yeah, if you really want to use git well, learn its internals. It takes some time but actually not even hard. After reading the Git Book once I was even able to implement my own git (of course without performance considerations).
Stopped reading after I saw this.
Trying to learn something from a bad article is worse than reading no article at all.