Install seat supports
Cut the seat supports and back supports to length.
Position each seat support beside a post with the top of the support 16½ inches above the ground and one end flush with the outside of the post. Drill a single ¼-inch hole through the post and the support, then bolt them together with a 6-inch carriage bolt. Adjust the support so it is level. Drill a ¼-inch hole and add a second carriage bolt.
More: where to start and what you'll need