First, you have to have zero self respect and have fallen upon really hard times while being so desperate for money that you would accept to lay down and have strange men's semen be released into your body cavities.
Then you have to realize that you could be in danger of being beaten, raped and possibly tortured and killed.
Once you accept those conditions, all you really have to do is dress like a whore and stand in a really seedy part of a city. There a John will find you and own you as he demands a good chunk of the money you make while having sex with strangers. If he catches you keeping more money than he finds you are entitled to, he will beat you. But, first, to own your sorryass, he will get you addicted to drugs so you depend on him for your next injection, just to survive.
It is pretty easy and you do not even have to provide your social security number or pay taxes.