Computer newbies forum: Reformat hard drive so can reinstall Sony VAIO laptop

What is the command to reformat a hard drive? I have a SONY VAIO laptop and its hard drive failed after just four years and no alternative other than to replace with a new hard drive. New hard drive was not purchased from SONY! The new hard drive was partitioned and I had to get a Windows "trialware" Operating System to try and get onto the laptop. Now that I don't have the proper "authentic" product key code to install the Windows after the trial was over, I cannot use the laptop other than in safety mode. This is why I intend to reformat the new hard drive now that I have rec'd the "recovery discs" from SONY that are supposed to reinstall the original operating system and its original software programs that I had when I originally purchased the laptop. I was told by SONY tech that since I had Windows XP "Home Edition" installed on the laptop since the hard drive "failure" they could not advise me any further and said I would have to reformat or figure it out myself since there is now new programs on the hard drive. Will reformatting the entire disc enable me to then use the SONY recovery disks and not see the wrong Operating System (Windows XP Home Edition) that was just erased? I was hesitant about "recovery disks" from SONY since having a new drive altogether, I thought it would need to "recover" original information from the SONY hidden partition but they said no, the recovery discs will reinstall the original operating system as well as other programs that I originally had. I just now need to know how I physically go about reformatting the hard drive. Don't care if it remains partitioned or not, just want it to work again!!!!!