There are several game engines that are both free and easy to use and to get started with. While Wintermute Engine is one of these, it's not the only one, and it is mostly suited for (and excels at) Adventure games or other types of point-and-click input games.
You might want to check out GameMaker or Multimedia Fusion (I prefer Game Maker, but haven't really used multimedia fusion so) as well as Wintermute. GameMaker has the advantage of letting you make games without really scripting, but rather drag and drop commands, even though I would recommend using the scripting available for learning.
You should also check out Unity 3D (and even maybe Adobe Flash and UDK) when you have gotten a bit more experience in the scripting part.
Wish you the best of luck!