Fellow sound designer here. I would suggest getting a copy of Reaper (free for trial) and getting a video/trailer from Blizzard or the likes and start playing around with it. There are many game sound designers using Reaper and I would say it has over taken Pro Tools and similar software. Get familiar with the tools and just have fun.

Try getting some free sound effects (check out the recent free Sonniss GDC sound effect pack torrent) and start putting them in. Make it how you want it to sound like and experiment with plugins, synths, and tools (there are some great ones that come with Reaper). Definitely read up on forums, books and anything you can find.

As you probably know, game sound design is so much more than just putting in sound effects. Understanding basic audio principles and theory helps a great deal. Recording, foley, mixing, editing, implementation are just some of the things game sound designers are responsible for. Get a cheap recorder and start recording interesting sounds you can use. Record some foley to match up with a video that you like. Once you get familiar with these, then comes implementation.

You can get a copy of Wwise or Fmod for free. Wwise has the advantage that Limbo is already attached to the engine and thus you can hear your sound effects in-game and experience what it is like to implement sfx.

This is a lot to take in, but try and see if you will enjoy it. There are some great schools for sound design. I was very much like you when I first started out. I didn't know much about sound design nor the tools or theory. I went to school for sound design and just learned these things and practiced. Later I worked in film and ended up in games.