I think it's kind of up to you. Do you want to talk in detail about it? Or do you feel like you want to talk about your feelings about what happened? What do you feel would feel helpful to you? You can start by just saying that something happened and leave it at that for weeks or months until you want to bring it up again. I've found that I want to revisit things multiple times and my therapist is welcoming of that. Sometimes he only gets part of the story until I'm ready to share some new part that feels especially shameful to me. I don't know how it works exactly, but I do know that there's a bit of relief in sharing. This is what works for me in therapy.