This works whether or not you are using GitHub.

  1. Get the free GitHub for Unity package on the Asset Store. Despite the name, it works for Git as well.
  2. In Unity, import GitHub for Unity into your project.
  3. Open Window, GitHub.
  4. In the GitHub window, click Initialize.
  5. If nothing happens, try to close and restart Unity.
  6. Add https://raw.githubusercontent.com/github/gitignore/main/Unity.gitignore to your main folder. This will make git ignore all generated files such as build files or cached files.
  7. Select the files you want to commit, enter a title to your commit under "Commit summary". Entering a description is optional.
  8. Click "Commit to [master]".
Once you grab the package in the Asset store, import it into your project.
They did a bad job at accessibility. The blank spaces are text boxes and "Commit to [master]" is a button.