Login Options

I have several questions about login options:

1. Is it possible to only allow users to login via social media authentication options, and NOT via WP accounts?
2. I have read elsewhere in this support forum that when a user registers via social media login, that it creates an account on the site. Does this mean that the user can or must login via this website account afterward? If so, how, if they didn’t create a username and password?

I may have more questions as follow up after I get your answers to these questions.