The Users module is part of the core set of modules.
It is used to allow users to sign up to your site.
This module can not be removed from the system, but user signups can be turned off.
The USER is the person, the PROFILE is where they put their stuff. One USER can have a number of profiles. The QUOTA is attached to the profile to define what MODULES are active there. Each QUOTA is a set of active MODULES.
screenshot of the user browser in the ACP
screehshot of the tools available in the ACP for the jrUser module
screenshot of the Global Conf page in the ACP to enable/disable user signups
Adding Form Designer fields to the signup form
To add another field to the signup form use the Form Designer