Sorry for this dumb question, I never used facebook, but what is the difference between your own webpage and a page on facebook? How do those facebook users automatically know that you exist when you are on facebook. They still would have to find you somehow?

Facebook's discovery is enhanced because they have more information about you, and so can correlate you and your friends information with information about the page to more effectively match you to that particular page.

For example, you are likely to like an event/business/venue your friends already liked, so facebook can suggest that business to you. Or you see in your feed that your friends checked into a certain event/business/venue, resulting in you being exposed to that.

All this happens without you even performing a search. And if you do perform a search, the top search result will most likely be correct, because it used you and your friends' information.