The authentication of your application is managed by Supabase.
The email and password authentication works out of the box when you completed the getting started guide.
You also get magic links as a free feature. Magic links are a way to authenticate users without a password. They are sent to the user's email address and when the user clicks on the link, they are signed in.
To enable signin with OAuth, you need add the configuration for the OAuth providers you want to enable in supabase. Learn more on how to do this in the official supabase docs.