A star or star within a dot on a map usually means that it is the location of a capital city, whether in a state or a country. The star is typically located on the legend in one of the corners of the map to indicate the symbol's meaning.
Map legends help to identify the shorthand and symbols on a map so the symbols do not take up too much space. There are many symbols in legends that serve the purpose of showing elevations, roads, city locations, boundary lines and sea level. Symbols help make maps more efficient and clean-looking.