So, to use ddd, download the .zip file. On the wii u, launch ddd, and put the IP of your PC (you can see it in GuiDDD, on the PC). On the pc, select the title dumper -> select the titledumper.exe file, full game or specific content -> where to dump -> start.
On the wii u, start the game you want to dump.
edit: the pc and the wii u have to be connected on the same network.