There are three ways you can make this sauce.

On the stovetop. Take a small pot or saucepan, combine all the sauce ingredients except the cornstarch, and stir. Take your cornstarch and make a cornstarch slurry mix with 1 TB of water until smooth, then pour into the sauce and stir until combined on medium heat let thicken string as needed until it's the thickness you want, remembering it will thicken as it sits a bit.

You can also use a microwave just add the ingredients the same way as above into a small bowl (microwave safe) or a pyrex glass measuring cup, microwave on 30 seconds intervals stirring after each one until the thickness you want is desired; this usually takes a few minutes.

If you're making some, say teriyaki tofu or soy curls, you can just add it to the dish on the stove and let it thicken as it sauces up the main dish, and it will thicken up as it cooks.