Windows 8 comes with a restore partition.
Slide mouse to lower right corner to bring up charms menu.
Settings -> Change PC Settings -> Update and Recovery -> Recovery -> Remove everything and Reinstall Windows.
You also have the option to create a bootable USB installation flash drive. Typically you need a 8 or 16 GB flash drive, though I've heard of one system needing at least 20 GB. You will want to do this if you want to delete the restore partition (usually to free up space if you have a small SSD).http://windows.microsoft.com/en-us/windows-8/create-usb-recovery-drive