To make a half double crochet stitch, you need to know the basic terminology: slip knot, chain and yarn over. If you need a recap on these, you can find it here. The half double crochet stitch can be seen as a mix between the single crochet stitch and the double crochet stitch. You will see what I mean soon…
Start with your chain. You can make your chain as long as you want or need it.
As you would with the double crochet stitch, yarn over once.
Go through the second chain from your hook and yarn over again.
Pull through the chain’s loop, but not the other loops on your hook.
Yarn over and go through all three loops on your hook.
You can continue your row in the same manner. When you reached your row’s end, turn your work and chain two. That’s it! You can now create patterns that require the half double crochet stitch. Tick that basic crochet stitch right off your list.