Deleting Everything Off an HDD?

[SanFran2700]

I'm new to the whole PC scene, being that i've played console basically my entire life. I've built my own PC (mostly for gaming). So I downloaded Steam OS, and I was wondering, when I get a copy of Windows, how do I delete everything off my HDD so I can download Windows?

Any help would be greatly appreciated! Thanks.

 

[Mattios]

http://lmgtfy.com/?q=Deleting+Everything+Off+an+HDD