Users are created by administrators at a site, and doing so automatically sends an "invite" to the user. See this article on adding a user.
By following the instructions in this invite allows a user to choose a username and password. Until they do so, they cannot log into HosPortal.
Sometimes users may ignore or lose this invite. Its simple to send a new invite.
1. Go to the users profile. You can see if a user has previously registered by looking at the "web" tab:
2. Chose "send invite" from the menu on the right.
3. An email will be sent to the user.