There are two main parts of the holster. The actual part that holds the gun, and the part with the belt clip. They are attached near the bottom of the holster. Think of it as a book, with the binding at the bottom and the open pages at the top. Your shirt tucks in to the 'pages' in between the gun and the clip.
It works great. I carry my Shield in a 'High Noon' Split Decision holster.