To do a double crochet do a yarn over, insert your hook into the next stitch, do a yarn over, pull the yarn through the stitch, yarn over, pull through 2 loops on the hook, yarn over, pull through the last two loops on the hook.

Yarn over means to wrap the working strand of yarn around the right needle, making another stitch.

No, they are not.

double crochet: Yarn over, insert hook into specified stitch, yarn over, pull through stitch, yarn over, pull through 2 loops on hook, yarn over, pull through remaining 2 loops.

half double crochet: Yarn over, insert hook into specified stitch or space, yarn over, pull through stitch (3 loops on hook), yarn over, pull through all 3 loops on hook.

Almost like you make the double crochet. Wrap the yarn over your hook or yarn over, put it through the loop and pull the yarn through, then wrap the yarn over the hook again and put it through all three loops on the hook

yarn over, insert hook into specified stitch or space, yarn over, pull through stitch (3 loops on hook), yarn over, pull through all 3 loops on hook