How would one make a model for the game?

I love the game and been addicted to it and I now want to learn about making models. But I can’t find a good guide or tutorial for this and I don’t know where to find the file to use for Charlie character model. The fbx file is what I mean and I’m not sure where I can find it in the game so…. Could someone help me by giving me a link or explaining how I would do this?