The Cooking Instructor is one of the many NPC you will come across on your journey. She can be found on the tutorial island as well as in Dorpat.
"I'm here to teach you how to do Cooking."
"First you need to catch some fish, Fishing Instructor can guide you you with that."
"After you have some raw fish in inventory, you can equip the fish by clicking on it. Equipped items have a yellow outline."
"To cook the fish, simply stand next to Campfire and click on it while the fish is equipped."
"Eating cooked fish restores health, very useful after a heavy battle."
"You can sell raw and cooked fish to the Fishing Master."
Disclaimer: This is word for word from the game, anything that sounds weird or is grammatically incorrect is purely the game.