The four holes are the "puck" system which uses a
Picture frame that the hitch fastens to. The center hole is the gooseneck prep.
If you look down in the holes you will see that they are rectangular cut, the picture frame has four matching pins which drop into those rectangular holes like a skeleton key. Each pin has a handle and is rotated 90 degrees and locks in place, that keeps the pin from coming up out of the hole.
The actual hitch attaches to the picture frame. There are different manufacturers and styles that use the puck system.
Here is one example.
I used the factory picture frame and an superglide automatic sliding hitch because I have a short bed truck and a 102" wide flat front old style FW.
Some FW have rounded front ends so some choose to not use a sliding hitch.