What happens if I already have an account on website A, and create a new account using Apple Login?

Hi!

I've wondered about this for a while and can't find an appropriate answer online.

1) Say I already have an account on website A with my email address (first.last@google.com), but I have forgotten about this. Then I go to website A and hit "create new account using sign in with Apple". My Apple ID is the same email (first.last@google.com). Do I now suddenly have two accounts on website A, or will the two accounts be merged since the email is the same?

2) Say I already have an account, and I want to start using "sign in with Apple" with this account. How do I do that? Like in question 1, just "sign in with Apple" and Apple fixes the rest? Or will there be an option for this after logged if this option is available?

Thanks!