Those are where the settings are. If you want open registration, turn off Manual Approval and Enable Email Confirmation. Then anyone, including tons of spammers, can easily join. If you want simply email sent, turn off Manual Approval and check Email Confirmation.
Which "admin" email do you refer. You mean your personal email that you have as an admin?
Do you mean the contact email that the "Contact Us" sends to?
Do you mean the email that the site's emails are sent from?