Someone whose job is cooking food and planning menus at a restaurant is a chef. Many chefs graduate from cooking school, while others learn cooking techniques by observing and working with experienced chefs..
The word chef often specifies someone who cooks fancy or expensive food — in contrast, you might call a man who fries burgers at a fast food place or a woman who makes grilled cheese sandwiches at a diner simply cooks. The chef is generally at the top of the food chain in a restaurant kitchen, the boss of the other workers. Chef is French, short for chef de cuisine, or "head of the kitchen."