Lords/Ladies and King/Queens who rule over land in a castle can hold court. They can also appoint court positions to help manage their kingdom. Court positions are Maester, Castellan, Marshal, Chancellor, Steward, and Spymaster. Regions near water can appoint Admirals to command their ships.
High lords and Kings with many subjects can hold court where they can hear inquiries, handle disputes, and petition artisans from their subjects and vassals.