Character abilities in Reunion come from Knacks - short statements about your character's capabilities. At game start you will have 8 of these; 2 from your backgrounds, 3 from the Mental or Physical lists and 3 from the Insider or Outsider lists.
Knacks are permissions - if someone has a knack they can just straight-up do the thing unless directly opposed by similarly potent capabilities. If you don’t have a knack, you can still do the thing but the GM is free to give you a cost (you can do it if you use up this/you can do it but it’ll do this back to you) or a compromise (you can’t do that but you can do this).
If a knack gives you an ability that can be used once per session, you may use it in downtime if you don't use it during a week's session.