The default installation of Joomla does not have search engine friendly URLs enabled. That means that if you click on the left menu to an internal page such as "Joomla! Overview", the URL of that internal pages looks like ...

Note that after the domain name, the URL has ...

/index.php?option=com_content&view=article&id=19&Item=27

with all these ampersands and equal sign symbols. This is known as the query string of the URL. Search engines are not able to derive useful information from these query strings.

We want, and search engines want, the URL to look like this instead ...

Note that the url now looks like ...

/joomla-overview

The URL contains words instead of query strings. And search engines can read these words and will be able to have more information about what your page is about. This is one technique of "search engine optimization".

In order to enable search-engine-friendly URL for Joomla, your webhost must have the necessary requirements. Then you need to perform these two steps.

1. If your webhost is running Apache, then perform this first step. In the base directory on your webhost where you had installed Joomla, you will find a file named htaccess.txt. Using your webhost control panel's file manager or an FTP client, rename that file to .htaccess (note that this filename starts with a dot).

2. Log into Joomla administrator and go to menu "Site -> Global Configuration" and under the "Site" tab, select "Yes" to the "Search Engine Friendly URLs" and "Use Apache mod_rewrite". And click the "Save" icon to save the new settings.

Note that you need to do a hard refresh of your browser in order to see the switch to the search-engine-friendly URLs.