We need to install git lfs before to actually work with the large files on the system
follow the instructions here: https://docs.github.com/en/repositories/working-with-files/managing-large-files/installing-git-large-file-storage
Once you're done installing it you dont need to do anything else and you can start working on it since we already have the .gitattributes and .gitignore files setup.
And that should be it to get start with working with git and unity.