Sample data is optional and if you want to install it, it should be installed when you create the database as described in the installation tutorial.
Installing the sample data will give you an insight into how to create products, categories,taxes,payment gateways, take some time to browse through the admin section and get an idea how Magento handles products.
Download the sample data
1. Download the sample data archive from MagentoCommerce.com.
Using a browser, download the latest full release archive file from MagentoCommerce.com (http://www.magentocommerce.com/download). The current sample data archive is v1.2.0 of the sample data. Don't worry that it's not the same version number as your Magento version number. The sample data is more generic and can be used for multiple Magento versions.
The archive file is about 10MB and is available in .zip, .tar.gz, and .tar.bz2 formats for download (each zipped archive contains exactly the same files and are provided in different formats just for your convenience).
2. Extract the sample data files from the archive.
When done you will have a file called "magento_sample_data_for_1.2.0.sql" and a folder called "media".
Step 2—Import the sample data into an empty store database
1. Create a new, empty database for Magento
If you don't already have one, create an empty Magento database using phpMyAdmin or whatever database management tool you prefer
Use the import function of your database management tool to import the data in the .sql file into your empty database.
If you're using an FTP program, open the media folder from the download you will see a folder named catalog move the catalog folder into the media folder for your Magento installation.
2. Set the permissions on the media folder to be read and writeable.
If you're using an FTP program, make sure the permission for the media folder and subfolders set to 755.