We run regular monthly events aimed at teaching beginners how to use the Linux command line. We generally run these on the last Tuesday of every second month. Check the events page to see when the next one is.
We use OverTheWire's Wargame Bandit as it provides us with a server to log into and starts off with the basics. We'll explain how to connect to it with PuTTY or your operating system's built in ssh client.
Not a beginner? Join us anyway, you can either help teach the newcomers, or race ahead and try your hand at some of the more difficult levels - as it's designed for hackers, there are quite a few levels that require you to think outside the box a little!