Here's how to double crochet two stitches together:

1. Yarn over: Start by yarning over your hook. To do this, bring the yarn from the back to the front, then wrap it over the top of your hook from back to front.

2. Insert the hook: Insert your crochet hook into the designated stitch where you want to decrease. For example, if you're following a pattern, it may instruct you to dc2tog in a specific stitch.

3. Yarn over and pull up a loop: Once your hook is in the stitch, yarn over again (wrap the yarn over the hook from back to front), and pull up a loop. You'll now have three loops on your hook.

4. Yarn over and pull through two loops: Yarn over one more time and then pull through the first two of the three loops on your hook. You'll have two loops remaining on your hook.

5. Yarn over and pull through the last two loops: Yarn over one more time and then pull it through the remaining two loops on your hook. This leaves you with just one loop on your hook.

You have successfully double crocheted two stitches together. This process decreases your stitch count by one and creates a smooth decrease in your work. You can continue with your pattern as instructed.