Open /sgadmin → add a location → a gizmo appears: move/rotate with the shown keys, sgGizmoGround snaps to the ground, confirm to save. Locations are stored in the database (socialgame_locations), not in files. Furniture (tables, arcade cabinets) is spawned by the resource - pick a spot with enough room and players will get a target/marker to start the game.
⌘ K