Need help with drive wiper

What exactly does it do?? I see it gives you an option to wipe free space only or entire drive. If you did entire drive is that like basically erasing everything on your hardrive?? like you have a fresh copy of windows now? There is also an option for setting how many passes you want. What is that for?? Id appreciate any info anyone has....thanks

WFS will overwrite all the free space on your drive, and leave all live files untouched.

Wipe Entire Drive will only run on a non-system drive. It will format the drive and then wipe all free space as in WFS.

How many passes? One is perfectly sufficient. More achieves nothing except hammering your disk.