How to Make a back-post double crochet stitch (BPDC)
First of all you have to understand that in this type of crochet you have to do similar to what you did for the front post double crochet. However the basic difference is that in front one you inserted the crochet from the front, however in this type you have to insert the crochet from the back side. So to do this you have to yarn over the crotchet and then go through the back to the right side of your stitch and just open up the front and then go back through on the right side of the stitch as shown. Once again put the yarn over the crotchet and then hole it through, now you have three loops over your crotchet so hold at front and then pull it through them. Now again yarn over and work around the next stitch and after going through it, hook it through the back and pull it right through over to the other side. Now again go through the three loops and pull the end thorough them and repeat it once more. This completes the step. That's it.