Can't really tell much from that picture, but I had a similar rack years ago for my Explorer - the hooks on the top straps hooked into the seam where the top of the tailgate snugs up to the vehicle itself, and the hooks on the bottom straps just hooked to the lip of the underside of the rear bumper. I would usually tie the excess/slack portion of the straps to the bikes themselve as an extra "peace of mind" measure to avoid looking in my rearview mirror and seeing my bike bouncing down the highway. lol
I no longer have my 2005 Liberty, so I have nothing to reference specifically for you. Good luck.