If you disable the self-registration module, users will be able to register and use the application without the administrator’s role. Self-registred users will have a student role.
For more information on how to enable/disable the self-registration module, please see this link.
Note that registration upon approval allows administrators to control access to the application. The user who submitted the registration request cannot enter the application, view any content, or make any actions until his request is approved by an administrator.