Cut the full-size pattern out, and tack it to the stock.

Trace out the part on the stock.

With a Jigsaw or Bandsaw, cut to within 1/16" of the line.

Edge sand to the line, ensure a smooth edge.

Cutting the stock to the length of the Seat Slats.

On a Table Saw, rip the slats to the proper width.

With a Router or Router Table, round off sides of parts as Instructed.

Sand with an orbital sander, followed by hand sanding.

Assemble.

Admire your work.