I liked the tip in the Mabel sew along, to mark your pieces with tape while you are sewing, so I did so with this project. This is telling me this is the front (or possibly back) bodice. I also marked my center front and center back as it is easier to do that now rather than after the pieces are joined. Those other lines are just drawing attention to the tabs I’ve cut into the fabric.
The instructions have your join the front and back bodices and the edges of the sleeves and then finish the edges. I find it so much easier to do BEFORE joining. This way I’m not serging in the round.