Darik's not kidding about the "nuke" in the name of his program: use DBAN only if you want to completely eradicate any trace of data on a hard drive. This is the ultimate in data shredding--there's no recovery once you've used it.
There are two work flows for using DBAN. When it loads, you can type "autonuke" and press Enter. From there, DBAN will show you the progress being made on wiping your hard drive's data. Larger HDs will take longer, of course. There's a more configurable option, as well. Hit Enter at the start-up screen, and the Interactive mode will let you select specific hard drives or partitions to be shredded. Use the space bar and up-arrow and down-arrow keys to navigate and select from shredding algorithm options, and press F10 to start the process.
Because DBAN loads before your operating system, there's not going to be much of an interface. If you're not familiar with the look and feel of DOS or changing your BIOS configuration, proceed with DBAN with extreme caution. DBAN must be loaded onto a CD, DVD, floppy disk, or USB thumbdrive to be used.