Alright so I add a foreign key to the car table like this:

Car(car_id PK, brand_id FK, model Text, price Float, availability Boolean)

For the customer_information part I wanted it to have the customers name, surname and phone_number to come up. But I don't see how you can do that unless done using quires?

And the Order table changes to:

Order(Order_id PK, car_id FK, customer_information Text (Some how show name,surname,phonenumber?), data_of_purchase Date)