Each action, like registration, purchase, even placing an order call an action to send notification, by email. To send any email, a email account is needed, at least one. At this section you be able to add an email account.
To properly configure email account you need to prepare such a details like host, port, user and password. We recommend using the domain email address. E-mails sent from the same domain as the store address inspire more trust among users.
Email display name will be shown as a sender of associated email.
The remote certificate is invalid / Secure socket options - usually, it's enough to make it enabled and second settings as Auto. However, if it doesn't work with your mail server you need to configure it.