Welcome to Rock, Paper, Skulk. If you like shooting aliens, and biting the faces off marines, then you've come to the right place.
We play regularly on Thursdays and Sundays from around 7pm (GMT+1).
Our steam group is here, so join that for event reminders and easy access to the chat room.
We use Mumble for our communication, and instructions for installing that are here.
After installing Mumble, you may also need to add NS2.exe to the overlay whitelist, so you can see who's in the channel and who is talking.
To do this, go to Configure > Settings > Overlay > Overlay Exceptions > Whitelist, then click 'Add'. Find NS2.exe (usually at Steam\steamapps\common\natural selection 2\ns2.exe) and add it.
Once you have Mumble installed and are connected to the RPS server, join the Games > Natural Selection 2 channel.
I'd recommend you install and join Mumble, even if you don't have a mic, because it keeps the group together and you get notified if we decide to change server or something. (Also you miss out on any really cool jokes that are being told).