It just finds errors, does not fix them. If it does find errors, there are really only a few possible causes: bad memory, overclocking, or bad motherboard. Since it avoids all other software, drivers, etc. (by using its own boot environment), it eliminates the possibility of other components being a factor.
You need to burn the ISO to a CD as in "Burn image to disc" and then boot with it in the drive, and have your BIOS set to boot from CD. It will then auto-load itself. You can't use the computer while it's testing.
- Oshyan