As you may know already, most files and documents can be recovered from hard drives even after being deleted and trashed. If you work with sensitive files, you'll probably want to completely destroy them. This prevents others from recovering them now or in the future when you dispose of your drive or system.
It works by overwriting files with a special sequence of bytes, so the original data isn't available. This technique is even accepted by the government and Department of Defense.
Once you install the gadget, you'll have an icon of a shredder on your desktop. To destroy files or folders, you'd simply drag and drop them onto the shredder. Once you click the confirmation, there's no getting them back.