I used the 3 step zig-zag to sew the lower edge of the facing to the lining fabric.
Cut the amount of elastic indicated on the pattern. I think should be elastic guide patterns.
Then the elastic and the leg edge have to be stretched together to evenly distribute the elastic to the fabric. I used a sturdy push pin into my table to anchor the one end of the leg opening while stretching it.
I don't have a good photo of the finished hems, but you can see at the bottom of this photo one of the leg openings all finished. I used a 3 step zig-zag to sew the slightly stretched elastic to the edge of the fabric and then folded the hem the width of the elastic and stitch it down with the same 3 step zig-zag.
My last words on this subject are DO LOTS OF PRACTICE SEWING ON SCRAPS!!!
so see what stitches work best for you.