Back Post Double Crochet Stitch

Final result - Supplies - Any size yarn - Recommended crochet hook size
To follow this Guide, you can use any size yarn you prefer, along with the manufacturer's recommended hook size. Worsted weight (4) acrylic works well to practice with. Gather your supplies and get ready to learn the Back Post Double Crochet stitch!
Before you make a Back Post stitch, you need to know how to make the basic double crochet. 
Yarn over the hook from back to front.
Insert the hook in the next stitch, pull up a loop (3 loops on hook).
Yarn over.-------Pull through 2 loops on the hook (2 loops remaining).
Yarn over, pull through the remaining 2 loops to complete a double crochet. 
To practice the back post stitch, begin with a row of basic double crochet.
Usually, you would chain 3 to begin a row of double crochet. 
Because the post stitch drops the base of the stitch to a lower level, you will need to chain TWO to make the height of a half-double crochet to begin a row of post 
Let's see the stitch worked in the same color 1st. You will notice how the base of the stitch blends in with the lower post, and is more difficult to see. Yarn over the hook from back to front.
Insert the hook from back to front in the next post space. This is the space between the current stitch and the next stitch.
Insert the hook from front to back in the following post space.
Grab the yarn with the hook.
Pull up a loop through both post spaces and up to the height of the previous stitch (3 loops on hook).
Yarn over, pull through 2 loops on hook (2 loops remaining).
Yarn over, pull through the remaining loops to complete the Back Post Double Crochet. Now, let's see the stitch made in a contrasting color.
Yarn over, insert the hook from back to front in the next available post space.
Insert the hook from front to back in the following post space. Notice how the work behind the hook will pull up when you insert the hook all the way around the post.
Grab the yarn with the hook. A look from the top side will show you how the work pulls into a "V" shape, with the post of the stitch creating the point.
Pull a loop to the height of the previous stitch (3 loops on hook). With the contrasting color, you can see the base of this stitch wrapped around the post of the stitch from the previous row.
(Yarn over, pull through 2 loops) twice to complete the stitch.
Repeat Steps 15 through 19 for the remaining stitches in the row, stopping before the last stitch. Remember, the post stitch drops the height of the stitch, so you need to end the row with a half-double crochet.
Yarn over, insert the hook in the last stitch, pull up a loop (3 loops on hook).
Yarn over, pull through all three loops on the hook to complete a half-double crochet.
If you want to create a fabric with single-sided texture, you will need to work a return row of basic double crochet stitches. You can see here how there is no raised texture on this side of the work.
Work another row of Back Post Double Crochet. With a color change, you can see how a row of post stitches will have a straight line of raised texture underneath it. If your row has a jog in it, check to make sure you have worked all the stitches correctly. You may need to tug gently to settle the base of the stitches into place on the post, until you've practiced the stitch more.
To create double-sided texture, make Back Post Double Crochet stitches in every row.
Continue practicing to perfect your stitches. When you 1st learn this stitch, it may be difficult to grab the yarn from behind the work without catching another stitch. You can hold the yarn against the hook with your thumb or forefinger if it helps, but you should learn how to work the stitch normally. Experiment with color changes if it helps you see the bases of the stitches, and check out the cool stripes you can create!
Make a Back Post Double Crochet Stitch by Jenny Guldin