Hey @huffman420bert36,
first off: the fan starts when there is performance demand (and therefore heat generated within the Mac), that should not concern you. The internal system takes care of itself here and makes sure that everything is within its operating limits.
There is a lot going on in the game and that needs CPU and graphics power. This is normal for almost every game.
If you want to check what is using your performance I suggest you check the "Activity Monitor", it's a built-in tool in macOS X.