For sure do NOT simply install the Duetwifi per the guide until AFTER you get it attached to your wifi LAN. Doing it before the install makes it easier to use a desktop PC or Mac. Otherwise you'll need to connect the Duetwifi via USB while it's in the containment. How to do that? Go to: https://duet3d.dozuki.com/Guide/1.)+Getting+Connected+to+your+Duet/7
I just followed the guide, then connected a USB cable to the Duet directly before giving it it's first dose of mains power and before attaching the back panel.