Joomla has several "Access Levels" and you can control who gets to see what based on their access level

For access to content in the front end of the website, there are 3 access levels:

• Public  - anyone can see these items
• Registered - these will be visible only if the person is logged in
• Special - these will be visible only to users who have been elevated above "registered" status by an administrator

So, when you set up the menu item that leads to that content or component, you can specify an "Access Level" for that menu item.  If you change the "Access Level" to "registered."  the item will show only if the user is logged in.  If not, they will not see the menu item at all.

These same access levels apply to the modules on your website as well.

If these three access levels are not sufficient for you, there are a number of Joomla extensions that will give you a much more comprehensive user system.

Take a look at these options in the "Group Access" section of the Joomla Extensions Directory.