Quick guide to the Doll Shop feature:

  To get started, on a computer look under Tam Explorer for the Doll Shop.  You'll see three options:  Buy Doll, Sell Doll, Convert Household Member.
Buy Doll-  brings up a list of every sim in your game who exists, but doesn't have a home.  If you want to buy your own created sim this way, you can place them in the world, make sure you have another household played that can buy them, then go back and evict the sim you wanted to buy.  After that, they should show up on the Buy Doll list.
Sell Doll-  sell a household member.  There has to be another sim in the household, teen or older.  You can't sell yourself.  When you choose this, two more options come up:  Premium Market and Foreign Market.  Premium Market will bring a bit more money, but you will have to switch to another household and buy them yourself, NPC's won't buy them.  Foreign Market will sell them automatically, but you will never see them again, the sim is removed from the game.
Convert Household Member-  does exactly that.  Again, you can't convert yourself, there has to be someone else in the household too.

  The Farm:  this is a text event where your sim undergoes conditioning to become a Doll.  It happens after you've chosen to either Sell Doll or Convert Household Member.  With the Buy Doll option, your newly purchased slave simply arrives at your door, already converted.  It is possible for a sim to escape during the event, or females can possibly end up pregnant.  Escapees simply come home again, with a moodlet that prevents them from being sent back for a while.  Nobody seems to have ever reported having their sim return pregnant though.  If you just want your sim to successfully be converted, just choose the first option every time the chance cards come up.
Edit:  Also, during the Farm event, the sim forgets their past life completely.  They won't remember any of their existing relationships, and will automatically quit their job.  This means, if you convert your wife (some crazy story arc about saving a rocky marriage?) you'll have to marry again.  Or your relatives won't remember that they're your relatives-- so, fair game!  And if you don't want that, cas.fulleditmode and re-establish those relations.

  Pink:  After being converted to a Doll, your sim's Fun meter will be replaced by a Pink meter.  The Doll needs to replenish this by having sex with their master, i.e. any non-slave member of the household that owns them (teen or older, obviously.)  If it depletes all the way, they will pass out for several hours, and wake up with a normal Fun meter again.  If that happens, they are no longer bound by the rules their master has set for them.  Also, if you let that happen, you can use the Doll Shop to send them for retraining, $5000.
Another way to replenish the Pink meter is with Stallion Juice.  It's under Tam Explorer>Spank Bank>Buy Special Cum.  It's horse jizz.  You need a lot, but your Doll can replenish their Pink by drinking that.  Useful if your Doll is a prostitute, they can stay out and make you more money instead of needing to come home and have sex with their master.  Especially since having sex with anyone outside the household will deplete their Pink FASTER.  In my experience, 2 customers, then must need to replenish Pink.

  Rules:  The owner of a slave can set some rules for them.  With the master active, click the slave, then choose Slave Management.  Under that will be two choices.  Clarify Sex Rules will bring up a list of choices:  Household (default setting), Specified Only (brings up a list of everyone the master knows.  Keep your slave to yourself, or choose to share with a select few friends but no one else, whatever you choose), Everyone, Prostitution (this choice automatically registers them as a prostitute, and if you change it to something else, will unregister them again), and Forbid All Sex (I don't know why you would want this).
Romance rules also bring up a list of choices, that affect whether or not they can become romantically attached to someone.  These can be a bit confusing, as the buttons are toggles.  Whatever the button says, it will do that if you click it, meaning that the current setting is the opposite.  Forbid/Allow Romance will let them become romantically attached to other sims (or not, if it's set to Forbid).  Romance Limit Tracker will limit how attached they get.  I set them to off personally, so the buttons would read "Forbid Romance" and "Enable Romance Track Limiter."  If it says Forbid, then the current setting is Allow.  If it says Enable, then it's currently disabled.  Confused yet?

  Something that gets asked a lot:  No, they will not automatically cook and clean or anything.  Yes, it's something we would all like to see.  If you have either Discover University or Parenthood, look up a mod called "Chores" by LittleMsSam, which will allow you to schedule times for your slave to automatically get busy cleaning.  Also there's an "Off-Duty" optional mod that comes with it, set your master as off duty and they will leave the chores for the slave to take care of.
Edit:  Thanks to Neodarkside, who pointed out this console command: sims.add_buff buff_Role_ServiceNPC_Maid  
That should make your slave act like a maid.  To remove that again, replace "sims.add_buff"  with "sims.remove_buff".

  And if you would like to just undo the whole thing:  nisa.unslave