Hold reset power on the Wii
Priiloader menu should come up. (If it doesn't you need to follow one of our softmod guides. Not part of it, the whole thing so you can do it right.)
In priiloader navigate to Install File
Select your usb loader.dol file
Goto priiloader settings
Set autoboot to installed file
Set Return To: to the system menu, HBC, or installed file depending on what you want to load into after you exit a game.