In truth, you are a producer and you are working for free.

The "work" is using the Facebook website or app. FB tries to make your work easy.

It is like particpating in a market study except you do not get paid for your time and participation; you are like a volunteer.

Allowing FB to show you things and record everything you do, how you react, etc.

Not really. Advertisers want access to us, not to our behavior. The goal is not to advertise to a behavior. The goal is to advertise to a person who will buy. Behavior is just a proxy to the real goal: selling something to a person.