The sheer runs the length of the dinghy, from stem to stern, and provides a lot of rigidity and strength to the hull. At the stern, it attaches to the side of the transom, at the stem, it fits neatly into the rabbet to form a watertight seal. Before any of this perfect fitting begins, the sheer looks more like an oversized board that runs out past the stem and stern, ready to be cut to length.
The shelf clamps will also end a bit short of the stem, as they will end up being cut back even further to fit the breast hook at the heel of the stem. The sheers are pressed tightly up against the stem and the rabbet line is transcribed onto the planks. A very careful cut is made using a fine toothed miter saw that will not wander as it cuts to trim the plank to size. I prefer to saw with the kerf just to the outside of the line drawn as it is easier to shave off a bit of endgrain as compared to trying to add to it.
A tight fit is preferred as it will form a tighter seal and prevent any water from slipping through the joint and into the hull. While the sheer should hopefully never be submerged (because we would be having bigger problems at that point) it is a good idea to make all the topside planks watertight.
The sheer on the starboard side is a bit low on the stem as compared to the port sheer, but this will all be trimmed up when the bow is finished. At this point, the sheers are screwed into place with copious amounts of polysulfide bedding compound to completely seal up the connection.
At this point, the sheer is now connected at the bow and stern, bedded and fastened with polysulfide and bronze screws. The dinghy is starting to take shape and look more "boaty".