During the Joomla installation process you will be given an option of installing default sample content.
If you are installing Joomla for the first time we suggest selecting the option to install sample content - you can always refer to the sample content for hints and tips as well as see how some things have been set up.
Your installation of Joomla includes sample data, if you selected to install it, which is designed to show you some of the options you have for building your website.
In addition to information about Joomla there are two sample "sites within a site" - these sites are designed to help you get started with building your own website.
The first site is a simple site about Australian Parks - showing how you can quickly and easily build a website by simply using the building blocks that are part of Joomla.
The Australian Parks website includes web-links, a personal blog, as well as an image gallery.
Once you have installed Joomla! you can keep the default content (if you accepted the choice to install the default sample content) - you can "unpublish" any content you no longer wish or need to see, or a decision you could make would be to delete the sample content later.
When you become more confident and comfortable with installing Joomla and using the features - you can always carry out future installations without any sample content.
If you choose to install the default Joomla content it is probably advisable to "unpublish" the default content articles.
Otherwise doing a "Google Search" will reveal default content pages of a Joomla install that contain an article titled the same as your Google (or other search engine) search query, when your website itself is nothing to do with Joomla.