They aren't necessarily "adverts" as you're imagining them. you can "sponsor" any post in the same manner as the advertisers.
you pay the same money and get the same choices.
So you have your army of fake accounts and use them to share misleading news stories and rants about thing that aren't true.
I write my "they're coming for your guns rant", with an accompanying meme or image and a link to a written for purpose fake new site. (as in actual totally fake sites, not just crap being reported by legit outlets). I can then pay any amount of money to push this post.
I tell FB what age groups and sex i'm targeting, what interests or "likes" those people should have, which geographical region they should be in etc etc. Exactly the same as a company running an advert. I then pay and facebook push my post into the faces of my requested audience.
Thus i'd target americans of voting age, who live in certain areas and "like" for example a certain politician/party page *and* the NRA page. Or who are members of anti-vax groups, or "pro life" groups etc.
Job done. My 10k fake profiles are all pushing similar stories to similar people fueling their particular fire.
They aren't adverts, they're just posts you pay them to push that are specifically designed to play on the morons fears.
Once done they will then be pushed to your audience who should then start sharing it organically themselves.
Think "Britain first" etc posting road signs with Arabic photo shopped on them and claiming they are in bradford.
It doesn't matter that it's nonsense, it's feeding their target audience exactly what it wants to see, which will naturally cause it to go viral.
No one with a brain believes it, but they aren't the target audience! The damage is done. you have a million angry racists convinced it's true, sharing it, discussing it, being outraged by it and seeing it as proof they are right. etc etc.
Now imagine a campaign of this during an election. Targeting those who are hard of thinking, and pushing EXACTLY the right buttons (religion/abortion/gun control/immigration/muslims/etc)
now please don't read me any poetry!