On the Users page you can manage the logins to your account. Users can be either administrators who can see and do everything or non administrators. When you create non administrators, you can manage the permissions for what levels they can see and manage. For example, you might want to delegate tracker management to various sub-levels within your organization. To do this, you'd create non administrator users and then click on the "edit permissions" and choose the level and contacts in the level that they can manage.