By default, all new accounts must be approved before the member(s) can log into their member profile and access restricted content. This lets administrators verify that the member(s) are a part of the community and they've registered with accurate information.
Administrators will receive a notification by default for all newly registered members, requesting that they visit the "Review center" to approve or decline the registration. Once a decision is made, an email is sent to each member on the account letting them know the outcome.
You can have the website automatically approve all new registrations via the "Settings" section of the Admin Control Panel, but this is discouraged.