How Do You Add Email Addresses?

How Do You Add Email Addresses?

I created an account easily enough by signing in with my google identity. Unfortunately, that is the not email I wish to use so I went to my account to add an email address. Unfortunately every time I enter the email address I want to use, it tells me I am entering the wrong password. I know my password. It's not wrong.

What do you do to effectively add email addresses?

Thanks,