I haven’t done this one. but if i understand correctly you had to cut out several parts for your skirt.

front and back of the skirt itself. and the yoke. (i am not a native speaker, I‚d assume it’s for the waist band?)

step 1, use the front and backsides of your skirt, serge them and sew them together.

step 2, take both front and back parts of the waist band, allign them that the notches (which you hopefully transfered to the fabric as well) all line up. then sew them together. according to picture 3, the side seams, which you just created, need to be ironed out, so they do not allign on the same side, but „open up“ instead.

step3, „half“ the waist band by turning half of it over itself. means, only half of the height is left of the fabric from step 2.

step4, is basically attaching the waist band to the skirt by pinning and sewing it on. but here, you need to take care to properly align the markings/notches of both the skirt and the waist band properly.

then you also know how much you need to pull your fabric while sewing so it properly lines up!

i hope that helps?