Hi Jim - are you talking about adding people as control panel users? You can use the drop down in the top right of your control panel (next to your picture) and choose "add a control panel user" - or you can edit their permission dropdown in their profile. 

If your site is only accessible to be viewed by people who are logged in you will need to have people set up a profile and log in before they can view it (they will not have control panel access unless you specifically change their settings in their profile)