Debian GNU/Linux is distributed freely over the Internet. It is possible to install it in several ways: from a CD, DVD, USB drive or Blue-ray disk, over a network, bootstrapped from within another Linux distribution by using Debootstrap, or from a MS Windows system. After the initial installation has been completed, further upgrades and maintenance are performed using built-in package management tools. It's possible to upgrade major software components, or even transition between releases of Debian without reinstalling the system.
How do I get Install Debian?
There are two main choices of installation media to meet your needs.
1. Download and burn the network install image
For those with broadband Internet access it is often preferable to use a minimal network install image, rather than download a full set of 650 MB ISO images. This network install ISO (called "netinst") contains just enough packages to install a basic Debian system. During the install procedure only the required packages are downloaded from the Internet, making it more efficient overall. A netinst iso image is around 180 MB.
If your wireless network card is not recognized by the installer you might consider doing the installation using a wired (ethernet cable) connection or installing using a different network card. In any case it may be preferable to install with a wired connection for bandwidth reasons or simply to defer wireless setup until after the initial installation.
If you have no way of establishing a network connection during the installation, then you will need to install using full installation CDs or DVDs.
You can download the network install image here.
2. Download and burn full the "CD/DVD" image
Although there are over 30 CDs (or 5 DVDs) in a full set, only the first CD or DVD is required to install Debian. The additional images are optional and include extra packages, that can be downloaded individually during the installation, or later.
You can checkout how to download CD/DVD images here.
Buy a set of CDs
The easiest way to install Debian is with a set of CDs bought from a vendor. There is a list of CD vendors:
Netboot via another Debian system
There is also the possibility to boot from another computer without needing to use CD/floppy media at all. All you need is a TFTPD and a DHCPD running on the install-from computer. This is called installing via "netboot".
PXEBootInstall - the manual for setting up a netboot server.
An updated installer that supports the newest hardware
DebianLive - Debian Live CD / DVD / USB
InstallFAQ - Including how to install unstable (sid).
FAI, Fully Automatic Installation
PackageManagement - Managing your system
Debian GNU/Linux Installation Guide (all architectures, stable branch)