If it's like others I've seen, two hooks would go in the loops on the back of the tire so there are two straps helping keep the tire from rolling backwards. The other, obviously, would go in one of the front loops and the ratcheting handle would draw it up tight.
FYI, their email address usually gets a response same day if you send it early enough. Or give them a call. It's a small company and I'm sure they will provide you with all of the help you need.
If you haven't left yet, please drape one of the harnesses over a tire and send a picture so we can see what is hanging off of each end. I'm not understanding why the two front loops seem to be in line with the rear loops.