CEmu is an software to emulate Wii U applications on PC and because it needs the game keys to start, a lot of guys don't know how to start it up, so this tutorial is for beginners with emulating Wii U games.
Download the latest version of CEMU from here. It works only with 64bit Windows.
Open up your keys.txt. You gotta remove "541b9889519b27d363cd21604b97c67a # example key (can be deleted)" and replace with the Wii U Common Key. You can find it here.
Next you have to find and paste the game key of your game, one key per line and it should look something like this:
541b9889519b27d363cd21604b97c67a # Game Title Key