For your code manager: Use the Ocarina code manager PC app
For using codes: Use Gecko OS
Basically, open a .txt file (with your codes) with the ocarina code manager. Pick the codes you wanna use, then select "export to .gct"
name it RUUE01.gct (if it's for AC:CF) and copy it to your "codes" folder on your SD card. Then on the wii, open Gecko OS and choose "load game"