There are many books and web pages that try to explain how Facebook works.
Alas, even the most topical material gets most things wrong -- confusing messages with stream updates for example. It doesn't help that the rules change constantly . Even Facebooks own, very limited, documentation is often dated. For example ...
... Your Page  can now post status messages - short text-only messages like those found on user profiles. Soon, these statuses will appear in fans’ News Feeds...
I don't know when this was last revised, but Page updates have been appearing in my News Feeds for months.
Ultimately, the only documentation on Facebook is Facebook. It's mind-boggling that this works for them. Suggests most of humanity has given up on understanding how the modern world works; which means that modern services need not be understandable.
If you want to know how something works, you have to experiment.
So I did this experiment on one of the Pages I administer. These Pages are "Liked" in my Profile.
I posted from two non-admin accounts (Emily and mine) and 1 admin account. I found.
- When a Person posts an update on a publicly accessible Page it is public and viewable to anyone on the net, regardless of one's FB privacy settings. This is obvious in retrospect, but I suspect most people don't know this.
- When a Page posts an update it goes to all subscribers.
- When someone you "Friend" posts an update on a Page you subscribe to you will receive a Wall (stream) update notice.
What I couldn't test is what happens when someone who is not a "Friend" of mine posts an update to Page I "Like". I suspect, in this case, I will not receive any Wall update.
So for the Pages I administer, if I want a status update to be received by all "Fans", I need to post it "as the Page" rather than using my personal account.
 In Facebook lingo a "Page" is something belong to an organization or celebrity or business. Individuals have "Walls". "Pages" have "Fans", regular people have "Friends".
 For example -- until today Facebook sharing has been symmetrical. If I "Like" someone they are notified of my shares and I'm notified of their shares. We have mutual access. Ok, I'm simplifying, the notification rules are constantly changing.