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