It's completely up to you as the teacher, Dan. Italki tries to limit the amount of teacher regulation to the very bare minimum. But you are in charge of your own hours, calendar, price and so on. It is also up to you as the teacher to prepare your own materials.
Now the word prepare here has a few different definitions. Personally, I like to mix it up. Sometimes I'll make use of worksheets, vocabulary tests and so on but sometimes I prefer to have lessons where we just talk about interesting topics such as relationships, exercise, diet, science, psychology, personal development and so on. This is important to develop fluency and I definitely still need to prepare for such lessons.
I use Zoom or Skype but some teachers also make use of the italki classroom.
I love teaching on Italki as it is INCREDIBLY user-friendly 😊
Feel free to ask me anymore specific questions.
Nick 💯