It's very simple. You just need to have a full copy of windows if there is no previous version installed.
To install windows, boot into the BIOS, and make the DVD drive the first boot device. Getting into the BIOS is usually done by tapping the delete key on startup. Once the DVD drive is set as first boot device, save the changes and exit.
The PC will restart, and you should see a message to 'press any key,' do so at that time. The PC will then start loading off the disc. Follow the instructions, and it's a fairly simple process.