We don't have a dedicated tutorial for this, but I'll explain it below :) Also, if you'd like to add one to your order it will come pre-filled in your tires.
Since, the process can be messy and you'll need a proper tool to remove the valve it might be a good idea to do it in a bike shop. However, if you can unscrew the valve you can add it yourself. Also, it depends on what kind of bottle or syringe it will come with (if you order from somewhere else). Once you open the valve just push down on your tire and keep your hand on it, that way you'll create a vacuum for when you place the sealant container. Once you place the container on the valve just remove your hand from the tire and start filling (make sure to have a dry cloth nearby if it spills). When you've finished filling, just screw the valve back on and pump the tire.