Learn Russian: Тираж обсуждается автором и редактором. - The print run is discussed by the author and the editor.

In Russian passive sentences, the person or thing performing the action (the agent) is put into the Instrumental case without any prepositions. This is the equivalent of using "by" in English, giving us "by the author" (автором) and "by the editor" (редактором).

Why is there a -ся at the end of обсуждается?

The -ся ending is used here to create the passive voice. The active verb is обсуждать (to discuss). By adding -ся, it becomes обсуждаться (to be discussed). Since the subject тираж (the print run) is receiving the action rather than doing it, this reflexive form shows that something is being done to it.

How do we know this discussion is ongoing and not finished?

The verb обсуждается is in the present tense and comes from an imperfective verb. Imperfective verbs focus on the ongoing process of an action, so this translates to "is being discussed" right now, rather than a completed past or future event.

Could we swap the word order and say Автором и редактором обсуждается тираж?

Yes, because Russian uses cases to show who does what. The Instrumental case on the people shows they are the agents doing the discussing, and the Nominative case on тираж shows it is the subject. Changing the order just changes the emphasis, with the final word usually carrying the most new or important information.