Hi Toastyblocks, welcome to the forum!
Gamebuino is based around Arduino, so much of the information about setting it up can be found on their site:
http://arduino.cc/en/Guide/WindowsAs far as programming language goes Arduino typically uses C or C++, but there are other options too. Most of the programs on the Arduino example page will also work with Gamebuino and will be enough to get you started:
http://arduino.cc/en/Tutorial/HomePage(Bear in mind though that the most simple app, BLINK, uses a LED connected to pin 13 which Gamebuino doesn't have, so you'll have to change it to 5 to blink the entire back light instead).
For the C language itself there are many, many resources across the net...I can't really recommend any myself because I learned C about 30 years ago, hopefully others can help here. Don't forget though once you've installed the Arduino IDE there is also a Gamebuino library for it which also has Gamebuino-specific demos that Rodot's put together for everyone.
And of course the final resource if you get stuck are these forums, it's what they're for!