If you're just looking to make a clean start with your system the best way is to reinstall from scratch. Formatting a drive wipes everything - you cannot selectively reformat. If you're looking to wipe everything with the intention of selling then you need to do rather more if you have any concerns about possible recovery of deleted private files.
Depending on how much data you have stored on the disk and to what extent you consider it might be private or sensitive you should run a forensic wiping of the disk. There are many packages to help you do this - google terms for "forensic wipe" to see what options you have.