Newspapers, realm announcements, laws and customs - all of these and many more can be published in-game in the form of publications. They share the same basic structure, but are applied and used differently.

Creating a Publication

At least one of your estates needs to have a library if you want to create a new publication. And that is all there is to it. If you have a place where it can be written and copied, you can create a new publication. If anyone will read it, on the other hand, is a different matter.

Roles in Publications

Once created, more people can be added to a publication in any of four roles (they can have any combination of them):

The owner(s) can change memberships and roles of the publication. You will almost always want to set up several owners because if a publication has no (living) owners left, it is effectively dead. Publication ownership is not inherited.
The editors of a publication can review, layout and finally publish new editions.
Authors can write articles, and edit their own articles until they have been published. They submit them to editors for approval, so you can make anyone interested an author because nothing will be published unless it is approved by an editor.
This is a passive role in that publishers don't need to do anything, but any new edition published by an editor will automatically be available at every estate of every publisher. Publishers have no influence on the content of the publication, so for a realm-wide newspaper, for example, simply make every lord of the realm a publisher and it will be available throughout the realm.