You might have to use your imagination a bit here but think of the table top as part B and the wood will play the part of part A.
As you have been following along it is obvious that the material thickness needs to play a part in where the drill guide goes. For this application it is no different. To deal with this we can first look at the "base" of the jig where there are some dovetail areas.
So it is reasonable to think that something must fit in those dovetails.
They give you one of these spacers so you have no spacers being good for 1/2" materials and add the spacer for 3/4" material. If for some reason you need to have work with thicker material they of course sell more spacers. I ended up getting the extras but have never actually used them.
Now you will also have to clamp the jig in place. Any clamp that will fit will work but if you can't get a clamp on then there is another option. They provide a hole where a screw can be inserted, do be aware of that screws length unless it OK to add a through hole...
Up next will be a small project. Once that is finished I have just a few other odds and ends to go over and we will be done except for questions and comments.