What do you think a non-gun owner, who has no guns in the household, should know about guns?
A gun, in and of itself, is only a tool. It requires both ammunition and a user to become useful. It's usefulness depends entirely on the user's intent and training. There are three types of guns, typically: Rifles, which are shoulder mounted and have spiral grooving (rifleing) inside the barrel to impart spin which stabilizes the bullet in flight for greater accuracy at longer ranges; shotguns, which are (typically) shoulder mounted and are smoothbored to discharge small pellets called shot in a disperse circular pattern at shorter ranges; and handguns, typically w/ rifled barrels useful at short ranges.
Most new firearms have some form of safety switch on them, with revolvers typically being the exception.
(You could go into greater detail if you desire, but most non-gun owners who have zero firearms in their homes and zero interest in them would probably not care to learn specifics)
Reiterate the Eddie Eagle program should they encounter a firearm.
? Should you offer any advice should they encounter a ner-do-well w/ a firearm... as to movement, cover, range of lethality, etc? I don't know.
...what should someone who lives with a gun owner know about firearms?
All of the above, + where and how they are stored/locked up, safety rules the gun owner practices, not to touch them unless invited (sad that I have to write that) unless you think it wise for them to know how to place each one, or each type, on safe, should they encounter one with the owner away (typically by assuring that the safety is engaged and/or the weapon is unloaded (which would require the firearm owner to educate them. Note: If I were King of the Forest, every Jr high and H.S. student would take a firearm safety class even if they were never around firearms the rest of their lives)