Content Display
Joomla has various built-in levels of user access to allow one to create site content for everyone but also have some content available only to certain groups.

Backend Access Management
Admin user levels control how much of the site someone can access to edit site content, change, add or remove extensions, update site menus, change site templates, and more.

More...
Joomla's documentation has more on all this - just click the following links:

User Group Access Levels Explained In Simple Terms
An overview of the various user group access levels in Joomla.

Users: Access Control Levels
An introduction to Joomla's access levels.

Front-end User Groups
There are four Front-end User Groups available in a standard Joomla! installation: Registered, Author, Editor, and Publisher. There is also Guest which is basically any site visitor who has not logged in. This article explains what they can access.

Back-end User Groups
There are three Back-end User Groups available in a standard Joomla! installation: Manager, Administrator, and Super Administrator. This page outlines how much access each has.

User Access Addons
There are Joomla extensions that will add to the functionality of Joomla access levels. You can find them by searching the Joomla Extensions Library. Please read reviews carefully as some work better than others, and some can be fairly complex to install.