Users will not be able to access the system until you add them. They cannot self enrol.
To add an individual to the system select “Manage > Users and groups” from the top menu and click the “ADD USER” button. You simply need to specify their name and an email address. They will need access to the email address in order to set their password and log in.
By default they system will invite the new user when they are created. You can uncheck the “Send invitation” if you would prefer to invite them later.