Well to start getting to the slave markets you need to enslave someone anyone.
Then get them to submit to you.
To start enslaving first you need room in your cell. You can get more room in your cell from socket.
If you haven't met socket yet you need to either start the portal panties task or decline it to meet socket.
You get this task from Alex after you get him the panties.
I have slaves that submit, though i dont see a prompt to do anything related to a market
You need to walk around outside of your cell now to trigger up to two events then you can go to the market.
