A kitchen or potager garden is a source of herbs, vegetables and fruits but can also contain ornamentals or just vegetables. It can be a large or small plot depending on the site and the amount of people it's servicing. My kitchen garden (above) is beside the deck which is the entrance to my kitchen so it's handy to pop out and cut fresh herbs and vegetables while I'm preparing meals.
I also have a vegetable and herb garden on the property but grow what we mostly use in the kitchen garden where it's easily collected at meal times. In my the garden I have a mixture of herbs and vegetables but no fruit which is grown in our orchard. The choice of herbs and vegetables depends on your taste. The vegetables I grow in my kitchen garden are: silverbeet, carrots, lettuce, shallots, tomatoes, beetroot, and sometimes kale. Herbs include basil, mint, sage, rosemary, thyme, lemon thyme, chives, and parsley. As you can see in the foreground of the picture I also grow Aloe vera which I always have handy to the kitchen in case of burns.
If you don't have the room for a kitchen garden to be grown in earth as I have done you can use pots to grow herbs, tomatoes, shallots, and lettuce. I never grow mint directly in the garden because it's very invasive so I have it in a pot on its own. Lemon balm is a lovely herb to grow close by; an infusion of the herb can help to calm the nerves and give a restful sleep.
The deck where my kitchen garden is has a roof so the garden, which gets sun most of the day, is easily accessed when it's raining and I can turn the light on to collect the herbs or vegetables at night if necessary.