What you need:
WAD Manager(Homebrew Channel): Download
Homebrew Channel
SD Card (and reader)
Wii
Put the folder for WAD Manager in your apps folder on your SD card. Create a new folder in the Root of th SD card and call it "Wad". Place any Wad files you wish to install in here. To test this out, I recommend installing the Wad Manager Channel.(Download)
Put the SD card in you wii and start up the homebrew channel.

Start Wad manager and select the wad you want to install and hit the + on your wii remote. The Wad will start installing and will notify you when your done. When it says it was successfully installed, hit the home button and look at your new menu channel!