system
Given the following post, respond as if you're commenting on Reddit:
human
[Warhammer 40,000] I am a moderately educated civilian on a feudal world. What is my understanding of the wider galaxy?

I am a young man living on a feudal world. 

I am not poverty-stricken and uneducated, but I am not insanely wealthy, either. Rather, I'm what might be termed as "upper middle class" by the standards of the planet, and received a good education.

Assuming that I know something about the Imperium, the Emperor and the wider universe, what exactly do I know?
gpt
You would likely know of the Imperium as a galaxy-spanning organization that protects your planet, much like you're expected to protect the citizens that live on your land.  You may know of a ship or two that regularly visits the planet, or of any orbital defenses that the planet possesses (if you have any), but the intricacies of inter-galactic politics would probably be nothing more than far-fetched tales and the occasional Crusade epic that lives on in your planet's central libraries.

More attention would probably be paid to practical skills like husbandry, local politics/history, and administration (plus any fighting styles that your local nobility prefers).  Machine cults would be limited to local branches or guilds that maintain planetary infrastructure or local buildings (waterwheels, irrigation, looms).  Mysteries of physics, plasma, and machine spirits would be unknown.

Dan Abnett's Iron Snakes book has a good intro based on a feudal planet, and hints a bit at what they know of the wider imperium.