A cool shot is usually a button on the blowdryer (depending on the model and type of blowdryer) that will have the blowdryer blast some cold air. This is especially useful for the end of your hair-drying, to both cool down your hair after all the heat that has been applied, and to help set the hairstyle that you’ve achieved with the hot air.
To use the cool shot, the steps are very easy:
1. Press the cool shot button (in some blowdryers it might be a switch or similar, it depends on the model so check beforehand)
2. Direct the airflow of cold air towards your hair, and use the blowdryer to go over your entire hair.
When you do this, the cold air will seal the hair cuticles, so that the style (like curls, for example), stays in place for a longer time. It will also cool down your hair so that the heat doesn’t cause as much damage (and it also cools you down, as the hot air can be quite annoying if it’s hot out!)