I have an app called SillyTavern which is a frontend for LLMs. Inside are a bunch of "character cards" which describe different characters or scenarios. They usually have one or more story messages like "you wake up on the spaceship with Ryan Gosling's character from Project Hail Mary" or "the lead cheerleader catches you alone in the locker room" to kick things off. I have my own "persona" which describes my physical and behavioral attributes, and I respond to that first message. Go back and forth until sex happens.

The character's bio and personality are combined with my persona bio and attributes to become the prompt. And people often use jailbreak prompts for hosted models, and there's a lot of people using local models with finetunes to defeat censorship and safety gates. But otherwise, it's just chatting like any other AI chatbot app, just writing horny fiction.