John is building bookcase 73 3/8 inches tall, he wants 5 shelves equally spaced. Where does he drill holes (space between shelf)? Shelf is 3/8 inch thick.

Do I add 3/8 for top and bottom? or is shelf 5 bottom? I do not have a clue.

I would add the top and bottom. In truth, the bottom is usually raised off the floor an inch or two, but I would ignore that here, we are not dealing with fine furniture. Remember now, holes are to be drilled in the center of where the shelf is to be. This is tricky, so draw a diagram.