Tables :: Adding A New Field When A New Record Is Added In Another Table

I have a table A in which I write down orders for cars. A record is an order. A single order may contain multiple cars in varying quantities.Each car has its components. Some cars may have some of their components common. There is a table B which indicates each car and its components required with their quantities required to build the car. There is a record for each different car.

Now suppose there is a new car we are going to produce so we need a new record in table B for the car and all its components. Also we need a new field in table A because people can now order the new car(in some quantity).

With form for table B we can introduce a new record. But how can we add a field in table A automatically after a record is added in table B?