By far the easiest way to install Debian GNU/Linux is from an Official Debian CD/DVD-ROM Set. You can buy a set from a vendor (see the CD vendors page). You may also download the CD/DVD-ROM images from a Debian mirror and make your own set, if you have a fast network connection and a CD/DVD burner (see the Debian CD page and Debian CD FAQ for detailed instructions). If you have a Debian CD/DVD set and CDs/DVDs are bootable on your machine, which is the case on all modern PCs, you can skip right to Chapter 5, Booting the Installation System. Much effort has been expended to ensure the most-used files are on the first CDs and DVDs, so that a basic desktop installation can be done with only the first DVD or - to a limited extent - even with only the first CD.
As CDs have a rather limited capacity by today's standards, not all graphical desktop environments are installable with only the first CD; for some desktop environments a CD installation requires either network connectivity during the installation to download the remaining files or additional CDs.
Also, keep in mind: if the CDs/DVDs you are using don't contain some packages you need, you can always install those packages afterwards from your running new Debian system (after the installation has finished). If you need to know on which CD/DVD to find a specific package, visit https://cdimage-search.debian.org/.
If your machine doesn't support CD booting (only relevant on very old PC systems), but you do have a CD set, you can use an alternative strategy such as hard disk, usb stick, net boot, or manually loading the kernel from the CD to initially boot the system installer. The files you need for booting by another means are also on the CD; the Debian network archive and CD folder organization are identical. So when archive file paths are given below for particular files you need for booting, look for those files in the same directories and subdirectories on your CD.
Once the installer is booted, it will be able to obtain all the other files it needs from the CD.
If you don't have a CD set, then you will need to download the installer system files and place them on the hard disk or usb stick or a connected computer so they can be used to boot the installer.