RT Linux HMI WiFi Dongle

fk5

I have a HMI Device that runs Linux 3.0.35-rt56, and I am trying to give it wireless internet connectivity using a USB WiFi Dongle. I am very much a beginner and I've been able to avoid the command line until now. I have reached the point of being able to SSH into the device via Ethernet from my laptop.
What WiFi Dongle do I need to buy, and how do I install the driver?
I've asked around, but everyone seems to have less info once I say its RealTime Linux.

Thanks