Numerous means very large in quantity. You wouldn’t use numerous to describe how many feet you have (just two), but you could use it to describe the infinite number of shoes in your closet.
The adjective numerous is related to the word number — which is no big surprise since it basically means "a large number of something." Use numerous to describe a copious or abundant amount that you can't give a specific number for. Numerous fans probably come out for the all-star game, for example. And numerous players wish they made the all-star team.