The Ophcrack LiveCD disc you just burned is a "bootable" disc, meaning it contains a small operating system and software and can be ran independent of the operating system on your hard drive. This is exactly what we need in this situation because you can't access the operating system on your hard drive right now (Windows 7, Vista, or XP) due to not knowing the password.
Insert the Ophcrack LiveCD disc into your CD/DVD/BD drive and restart your computer.
The initial screen you see after restarting should be the same one you always see immediately after starting your computer. There may be computer information like in this screenshot or there may be a computer manufacturer logo.