When you first install a Joomla site, the last page of the installation gives you an opportunity to Install Sample Data. With this there is a list of the different types of sample data available.

All of this Sample Data is English and if you are going to have a multilingual site - the 1st radio button says that it is required to select None for this instance.

Screenshot of the sample data during installation

What is Sample Data?

The sample data will install Articles, Categories, Modules, etc that will give a first time user some clue as to what each component will look like and how it will function.

Should I install the Sample Data?

Choosing to install Sample Data is a good idea IF you are just installing a learning site.

You don't want to install Sample Data and leave it in there. The search engines will index this data and that is bad for SEO.

You don't want to install Sample Data if you already have a good understanding of the roles of the components.

You don't want to install Sample Data if you are developing a site for a client then hand off the site to him without removing the data. This will confuse the client to no end.