To allow a site user to add other users on the site, you need to make sure that the user is a member of a user group that has permission to create users. The permission that controls this ability is called "Can create a new user." You also need to make
sure you have a link to "Profile" in the navigation of your site. Profile is found in the Standard Items. Once the user clicks on
the profile link, they will see a tab called "Users." There is an "Add User" button on that page.