How do I clear all the stuff on my computer?

no no, just buy a new WINDOWS ( xp/vista/7 ) and format your pc , its easy , just search the steps online , or give it to somebody who’s good at it , and you’ll have a brand new pc :D ( p.s you can wipe the c: disk , the d: disk , or both ) hope i helped :)

I said it’s a mac.. but thanks anyway

Deleting files and even formatting the disk will not overwrite all the data on your disk. What you really need to do before selling it is to wipe the disks. There are various programs out there to wipe disks but one that is free and excellent is DBAN or Derik’s Boot And Nuke. You boot off the CD then choose how thoroughly you wish to wipe your disk ranging from a complete overwriting to a multipass Department of Defense strength disk wipe. If you have a fairly recent Intel based Macintosh you should be able to use DBAN but if you have an older PowerPC based Mac than it is going to be more of a challenge. If you can’t wipe personal information off of the disk you shouldn’t give it to anyone else. Worst case consider removing the hard disk and selling your Mac without a disk. Disk drives are cheap now so your buyer should be able to pick up a bigger faster drive without spending a lot of money.

oooooo sorry i didn see it :S .. sorry