There are already plenty of goodguides for wiiufrii so we will just link them here. pick one. For newbies, USBHelper is the easiest.
USBHelper+USBHelper Launcher:
https://wiki.agilly1989.xyz/books/wiiu/page/usbhelper-usbhelperlauncher
FunkiiU (Requires Python):
https://gist.github.com/Irastris/31766414a981a056d49c1242a019829a
JNUStool (Requires Java):
https://wiki.agilly1989.xyz/books/wiiu/page/maschells-toolkit#bkmrk-jnustool