You have learned how to create a new empty repository on the GitHub web server. You then cloned it to your local computer.
You also checked to see that this clone had a link back to its remote origin.
If you have simply downloaded and decompressed the ZIP file, you would not have the .git folder, nor would you have the remote links back to its GitHub origin.
The .git file actually contains the entire history of changes to the project repository files, and using different Git commands, you can update the folder to re-instance any of the committed snapshots for the project repository contents.
The special file called .gitignore lists all the files and directories that are not to be archived. At the time of writing, here are the contents of files that do not need to be archived (they are either unnecessary or can be regenerated when a project is loaded into Unity):
[Ll]ibrary/
[Tt]emp/
[Oo]bj/
[Bb]uild/
[Bb]uilds/
Assets/AssetStoreTools*
...
