put DVD/CD of the OS you want to install, boot your laptop from DVD/CD(you have to go to BIOS setup for changing the boot device, generally 'delete' or 'F2' or 'esc' pressing at startup will do.), follow the instructions... that's all
don't forget to change boot device again after formatting.
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If you are trying to format the hard drive completely for another person, then simply place in a operating system install disc. During installation, pick a clean install. It will ask you which hard drive you would like to install to, and at that time you will be able to format your hard drive. You may continue to install the software if needed, or you can simply quit the installation process there.
If that is not an option, you can try hooking the HDD up to another PC via SATA and format the HDD under My Computer in Windows.