That's kinda tough, there are multi-semester college courses on the same subject. But the BSA is not looking for some kind of manifesto on the historical derivation of States rights vs. Federal supremacy vs. the Individual.
Keep it very simple and basic, something like: The Federal Government's powers are to conduct affairs of nationwide impact (like the Commerce Clause, the power to conduct international diplomacy to include national defense and treaties with foreign powers and entities, to guarantee individual rights set forth in the Constitution as amended, and to provide courts to resolve conflicts between the States or that cross State lines). The States make and enforce laws to govern what happens within their own territory (like their own criminal law for most types of crimes, business and commercial transaction laws, laws about how land is sold or how it can be used, and most fish-and-game law). Both of them have the power to impose taxes, to pay for the systems to enforce their laws or execute their powers. If there is an overlapping area and the two types of law come into conflict (Like, say, migratory game birds that fly over many States each and every year and so affect multiple States, but would also be subject to a particular State seasons and limits as game while in that State), then the Federal law trumps the State law.
