Question: I found two plastic pieces that appear to match the shape of the wing roots. What are these for?

Answer: These are a bonus component that was added to this model. Usually they appear on one "sheet" of plastic and can be cut out and mounted by the modeler after assembly. These are wing root fairings or covers and serve to provide a cleaner seal between the wing roots and the sides of the fuselage. They can be cut a bit large initially and then trimmed to fit.

Supplementary Information: Are they absolutely necessary? No they are not. They provide a better seal and look nice but they are not mandatory for flight.

What adhesive should I use to mount these? Always test any adhesive on a small out of view area of any painted or plastic component before proceeding. We generally recommend Pacer Dap-A-Goo for this type of component in this type of application. Dap-A-Goo is a silicone like material that has a solvent base rather than acetic acid and it dries quickly, fuel proof, relatively clear and best of all it sticks to just about any plastic and stays slightly flexible. Remember... ALWAYS TEST FIRST!