The Roster section of your site lists all of the members that belong to your community.

Searching Members
By default the Roster only shows the Active members on your site. If you click the Search button, you can choose to instead show Inactive members or Deleted members. This can be useful if you need to reactivate a member who was removed in the past.

Adding New Members
While most communities will use the Applications feature to add members, you can bypass the process and simply invite members if you need to by clicking the Invite Member button. This will take you to the Invite Member form:

From here simply enter their email address and the name they should be displayed as, and a member will be created on your site for this user and an email sent out to them for them to setup their account.

Editing Members
With the Members Admin permission you can edit members on the Roster page, and depending on whether they only belong to your community, you may be able to edit their email and password. This is designed to help you get new members onto your site that may be having trouble.