I'm trying to figure out how to create an editable field that holds a Site-wide message ex: "Welcome to our site" that displays on every page. I want to be able to edit the field in one place and update every page with the new message without changing any code after it's working. Even if I stuck that field on some random page, I still don't know how to access the fields of one page from a different page, especially if the pages are not direct siblings or descendants. The kind of information I would need to build a menu would probably be useful to find out how to build this site-wide message.
Can someone point me in the right direction?
Edit: I've discoverd Menu(1), Children and ChildrenOf() controls
Is there a page that lists all the default controls/functions that can be used in a template?