Back post double crochet
US back-post dc wraps around the post from the back, pushing it away from you.
Counted practice swatch
Make 15 dc. Keep the first and last stitches as plain dc; work back-post dc around the inner 13 posts.
Work the repeat
Yarn over, insert from back to front beside the post and front to back on its other side. Pull up a loop; yarn over through two loops twice.
Read the fabric
Keep the strand behind the fabric during insertion. After turning, the former back face is in front; read which face needs the recessed post.