how to draw porn

Learn the basics of drawing if it's not already the case: shape, perspective, colors, volumes, etc...
Learn anatomy, it's the structure of the human body and you're going to need this a lot, all the time. (try to draw real humans, see what limbs can do, what posture does work and doesn't, etc...)
Learn things such as poses, angles, how bodies interact with each others.
Don't worry it's less tedious than it sounds, you basically have to draw things to try to understand them.
Finally, don't hesitate to use references when you have a specific idea, it's easier to draw when you see the poses than trying to do it from your mind alone.

Decide if you want an alt account or not. Some opportunities will close off themselves to you if you do porn art. Some will open. Ultimately it’s up to you.
Start off by drawing what you like. what kind of people/bodies do you like?
What kind of sexual acts just make your junk explode? Start there, now whether or not that’ll be what you enjoy, who knows. BUT it’s some place to start.
Now, how do you actually want to draw? Do you want to draw very detailed bodies or more simplified? This will heavily influence just exactly how well versed with anatomy you will need to be. The more detailed the more anatomy practice you will require. There are artists like Minus8 that don’t go very detailed but still make exceptional lewds and you have some that are like Yang-Do who would require more, so it’s largely up to you on how much detail you really want/need.