Step 2: Add vanilla.
Now that your simple syrup has cooled down a little bit, stir in a tablespoon of pure vanilla extract.
Now use a funnel to pour your syrup into a storage container of some sort. A plastic salad dressing bottle works well since you'll need to be able to pour the syrup. Make sure the container is big enough. The one I use is 600 ml.
Store it in your refrigerator.
You don't want it to melt the ice in your soda, so it's best to chill it before use. I like to give it an ice bath if I want it for immediate use.