The Food made by the Chef provides temporary bonuses when eaten, but this can only be done outside of a combat. Usually, meat dishes will give characteristic bonuses, fish dishes will improve damage, and drinks will improve resistance.
To a good Bow Meow go the spoils
First of all, as a Chef you will be doing a crafting profession. Previously a permit was needed for this profession and you were unable to use harvesting professions; however that is not the case anymore due to an update.
The Chef can make dishes using various ingredients. Farmers, Trappers and Fishermen will supply the Chef's main ingredients. The main advantage of these dishes that you will be making will be the temporary bonuses they can give to anyone who consumes them outside of combat.
Generally speaking, meat dishes will give characteristics bonuses, fish dishes will give elementary damage bonuses and the drinks will improve elementary resistance. Once you've got all the ingredients together, you will need to go to the nearest Inn and cook your dish on the Stove.
Once you've advanced a little further in your career, you will no doubt pick up a few regional recipes, reserved for Chefs from certain Nations.