Both Joomla and Wordpress have the ability to add unlimited usergroups (Joomla) or siteroles (Wordpress) your users can be member of.
Creating custom groups/ siteroles allows you to show/hide certain content from your website for different users.
How to add Joomla Usergroups
Step 1: Add a group
"Backend -> Users -> Groups" and hit 'new' button
Name your group and select the parent usergroup. (selecting 'Registered' here makes the group the same level as 'Author)
Step 2: Add to ACL level
You are not finished here as Joomla uses ACL levels for modules and menu items.
"Backend -> Users -> Access levels" and click on the ACL level you want to add the newly created group to.
"Registered" means view
"Special" has content edit privileges
Check your custom usergroup and hit 'save'.