CUDA wont "help" you write a game. If you need help then you need to look into programming. You have to have a pretty solid grasp of programming (mostly C++) to make a game. And you will also need to know how to use DirectX or OpenGL.
There are a lot of free 3d engines out there that are already written for you, you just have to make the 3d models and textures, the levels, the weapons and the scripting and you can have a game.