Instructions
Download WAD Manager.
Double-click the archive and extract the contents to the root drive of your SD card.
Double-click "Computer," then double-click the SD card. Right-click and select "New Folder." Create the folder and name it WAD.
Paste the WAD or WADs you downloaded into that folder.
Insert your SD card into the Nintendo Wii and launch WAD Manager through HomeBrew.
Choose the IOS to use to install the WAD. Typically 249, the default, works for nearly any WAD. Select where the WAD is located on your card, then press "A" to install. Exit WAD Manager to complete the process.