Participate in worldbuilding

The GM is responsible for the world at large. But as you create your character, your playbook will prompt you to define things about the world: about the god you serve, about the troubles you've seen, about the NPCs who live in Stonetop. Choose options and make up details that you find interesting and compelling.

As you introduce your character, the GM will ask you questions. Lots of questions. Some of these will be about your PC specifically ("Do you know how to read?") but others will invite you to add details to the world ("Who, if anyone, did this job before you?"). Once play begins, the GM will continue to ask questions and build on the answers. They'll ask your character questions that help shape the world, questions like:

• "Rhianna, who taught you how to hunt and track?"
• "Blodwen, you live with your mother, right? Any siblings? What's the place look like inside?"
• "Vahid, you've met Brennan before, what's his most distinctive feature?"
• "Caradoc, what have you heard about the Quiet Twins and how they came to haunt the Stream?"
• "Vahid, what have you noticed that all the missing children have in common?"
• "What's the most striking detail about the Flats in early spring?"
• "Caradoc, when you got back to Stonetop, whose reaction surprised you the most?"

Answer with enthusiasm, with color and life! Think about what you know about your character, what you know about the assumed setting, what other players have already established. Steal cool ideas from books or comics, from shows or movies, from other games, from real life. Add details that you want to see in the game, that you're excited about! Give answers that you think are cool and interesting, and you'll automatically be engaging with the fictional world.

With that said: don't overthink it. The best answer is often the obvious answer, the first thing that comes to mind. The first thing to come to your mind is often a surprise to the GM and other players, something they'd never have thought of, and thus you're helping them play to find out what happens.

If you find these sorts of questions offputting or even stressful, consider why that is. Talk to your GM about it. If you don't like being put on the spot, the GM can ask you a question and then move the spotlight, giving you time to think. If you feel like you're being asked to do the GM's job (author the world) and that takes away from your fun, the GM can ask you fewer questions that involve worldbuilding and more questions about your PC's current thoughts and feelings.

But also, it could be that you're just not used to it. Many roleplaying games have a very strict line between the player's job and the GM's job, and Stonetop intentionally blurs that line. If worldbuilding isn't something you're used to doing, give it a try. Stretch yourself! The more you participate in worldbuilding, the easier it becomes.