If your machine needs iwlwifi (as does my older Lenovo), for Debian:
Make sure "nonfree" is in your sources.list
apt-get update
apt-get install iwlwifi
Simple as that. Ceni or wicd can help identify and set up your
interface(s) but any required non-free firmware must first be installed.
Some newer devices might need a newer kernel.
Debian does not ship non-free by default (iwlwifi). That does not
necessarily mean it is difficult to install, if needed.
https://wiki.debian.org/WiFi
David