It will be necessary for the system to boot from the CD. If that doesn't occur (assuming the optical drive is working OK), there will either be a keypress to choose the boot device (often listed on screen at start), or you'll need to enter the BIOS setup and temporarily alter the boot priority to have the optical drive first.
Is the disc a system restore disc belonging to the system? If it is and it's from a major manufacturer, it may be pre-activated and resolve that issue. If not, the fresh install will need to be activated anyway. Before proceeding with a fresh install of the OS, you should consider having in reserve the correct drivers for the hardware, and knowing the product key for the OS and any other installed software that requires one. You will of course also need the source media for that software, such as the games, to be re-installed.
Edited by Platypus, 03 December 2015 - 07:03 PM.