https://gbatemp.net/threads/guide-noob-guide-to-wii-u-hacking.451297/
https://gbatemp.net/threads/the-definitive-guide-to-wii-u-hacking.396828/
https://gbatemp.net/threads/the-definitive-vwii-hacking-guide.425852/
Go through all three and read everything (great source of information)