To reboot simply means to restart. Click the start button and click "Turn off computer". Select the restart option. That's a reboot. Your boot device is the first hard drive, CD, DVD or other memory device that is accessed when you start or re-start your computer, which contains instructions the computer understands and processes, such as starting XP.
windows xp boot device is CD-ROM. In the windows setup select the boot device priority from the boot menu and select CD-ROM as the first boot device. After that insert the windows xp cd into your cd drive and reboot your system.
This is typically your internal Hard disk. The machines internal setup can also make your CDROM,floppy disk or USB boot as well. All newer machines are setup to boot in a "Boot Order" first the CD, then the USB, then the Hard disk. The machine should boot regardless... unless the boot devices have no data or media installed.