Here's how to half double crochet two stitches together:

1. Yarn over: Start by yarning over your hook (YO), which means wrapping the yarn over the hook from back to front.

2. Insert hook: Insert your hook into the specified stitch where you want to make the decrease. This could be the next stitch or as indicated in your pattern.

3. Yarn over and pull up a loop: Yarn over again and pull up a loop through the stitch you just inserted your hook into. You should now have three loops on your hook.

4. Insert hook into the next stitch: Yarn over and insert your hook into the next stitch, the one you want to decrease with the previous stitch.

5. Yarn over and pull up a loop: Yarn over and pull up a loop through the second stitch, which will give you five loops on your hook.

6. Yarn over and pull through all five loops: To complete the hdc2tog, yarn over one last time and pull it through all five loops on your hook.