OK, these two responses really help. Jerry's spells out how someone can buy access for an ad or other material to a targeted selection of users. Presumably the data FaceBook uses to comply with Jerry's purchase is proprietary. They own that data, and they sell a subset of it to Jerry for a fee, or rather he gets to use a subset of it for a fee. I assume Jerry has to have a checkable identity to buy the data, which explains the need for that poor shlub who got busted by Mueller for selling phony on-line IDs to whatever that company's name was.
Which brings me to Dean the Librarian. S/He talks about 'bots, which I assume is short for robots. Does whoever controls and launches the 'bots [the Sorcerer's Apprentice, in the great old movie Fantasia] need to buy data from FaceBook? How else can the controller shape the audience?
I am getting closer to understanding, but I am not there yet.
Let me explain the hunch, or intuition, behind all of this. It occurred to me that maybe the FaceBook executives could quite easily control the use of their platform, contrary to what they said to Congress, but that it would cost them money in lost revenues to do so. Is that so?