STEP 9 page 49: As you can see the template is shy of the full height of the trouser unit, which is a drafting error in my part. However the angle is correct, so use your ruler to extend the line prior to marking the placement line. I found it easier to turn my unit through 180 degrees to mark my line; Place your trimmed background piece on the placement line and pin.
Stitch a 1/4" away from the placement line and set the seam before pressing the side piece open; Then turn your unit to the wrong side to trim down the background piece (as we did for the goose and swan beaks); fold back the background piece to trim away the back layer, then press open again.
STEP 10 page 50: Trim away a 7/8" strip from the left-hand side (or crotch!) of the unit, before adding the 1 7/8" x 6 1/2" blue piece to make the left trouser leg; mark a placement line for the outside edge of the right trouser leg as before.
Join a trimmed background piece and pin stitch press and trim as before; to create the leaping effect, mark the bottom of the trousers with the template and repeat the process (STEP 11).
Here's a photo of the back of the trouser unit showing seam direction and a photo of the front once the background piece. The 'waistband' of the trousers should measure 2" so that it will line up with the tunic.
I appreciate that this seems like a lot of steps, but once you've made one pair you can chain-piece the rest. Happy tailoring,