If you're using the barn wood planks, cut them to size and skip to the next step. Cut the 1x6 boards to size and drill 3/4" pocket holes according to the diagram. Attach them together with 1 1/4" pocket hole screws and wood glue.
Cut the headboard cleats to size and attach them to the headboard planks with 1" brad nails and wood glue, from the cleats into the back of the headboard planks.
Cut the headboard side trim to size and attach it to the ends of the headboard. If you are using 1x6 attach with 1 1/4" pocket hole screws and wood glue. If you are using barn wood planks, attach the trim with 1" brad nails and wood glue.
Cut the top and bottom trim pieces to size and attach them the same way.
Attach the headboard to the posts with 2" wood screws, from the inside of the headboard trim, into the legs.
Cut the headboard and footboard top rails to size. Drill 1 1/2" pocket holes at both ends and attach them to the legs with 2 1/2" pocket hole screws.