what does ( Common sense is instinct, and enough of it is genius) Mean?

Probably just mean "Experienced". People with enough common sense to recognize any given situation for what it represents is probably have enough live experience to do so, or pretty smart, or both.

That means that everyone is born with common sense. (If we weren't, it wouldn't be "common".) If you have more common sense than the average person, then it's no longer called common sense, you are considered to be a genius.