What is the post of a double crochet stitch?
The bottom part of the stitch — that actually makes up the fabric — is called a post. So when you’re working post stitches, you work around the post instead of into the top of the stitch, inserting your hook into the space between the posts of the previous row.
What is the post of a single crochet stitch?
Since a single crochet stitch doesn’t really have a post to work around, you’re going to insert the hook into your normal single crochet stitch, under the 2 loops. But instead of yarning over and pulling up a look, insert the hook from back to front under the 2 loops of the next stitch. That becomes the ‘post’.