Working around the front or the back of a post of the previous row gives an interesting raised ridge on the crochet fabric. Around-the-post double crochet is worked by inserting the hook from the front or back and around the post of the double crochet of the previous row. While this technique is commonly worked in double crochet, the same methods can apply to single or treble crochet.
For these instructions, we're going to show you how to pick up and work around the front post in double crochet.
Yarn over, insert hook from front to back to front around post of corresponding stitch below, yarn over and pull up loop [yarn over, draw through 2 loops on hook] 2 times.
Here's a video demonstrating how to make post stitches in crochet.