Before we start worrying about managing members we must first decide how members actually register on your community.
In the AdminCP go to System -> Login & Registration, under the registration tab you will see a page with various options.
Allow new registrations = You might want your community to be completely private where you manually create new members. If that is the case then just completely disable registrations. When do you this, the Sign Up link on the front end automatically hides.
Validation method for new accounts = By default this is set to Email Validation which requires new members to validate their email account before completing their setup. You can also allow for administrator approval if you want tighter control over your membership.
You might not want to enable administrator validation of new members unless you really need that level of control as often people will lose interest if they have to wait around for approval to join your community.
We also provide COPPA support for clients who need to comply.