The table lists all your users.
If you are administrator of the current account, you will see all the users that have access to at least one environment of the account. If you are not an administrator of the current account, you will only see users that have explicit access to the current environment.
To manage a given user, open its detailed view by clicking on it.
Add a user
Click on Add a User to add a new user to any role for your account as described in the Add a User chapter.