Instinct
Your instinct describes how your PC tends to behave, for better or for worse. If you demonstrate your instinct in play, or struggle against it, you get to mark XP at the end of the session.
For your first PC, choose one of the instincts listed in your playbook. If you have played before, and none of the listed instincts feels right, feel free to pick an instinct from another playbook or make up a new one.
Your instinct can change during play. You'll be prompted to consider doing so each time you Level Up, but you can change your instinct any time it feels right to do so. Pick something else (from your playbook or another), or make up a new one. Just be sure to let the GM and the other players know.