You will have 3 tables here
table: make with make_id
table: model with model_id and make_id
table cars: with car_id and model_id
When you add a car to the database, you will have two drop down menus, make and model
you will have to select a make from a drop down menu of make, and then a new model drop down menu will show based on the make you select. that model drop down menu has model_id info. so when you add the car, the model_id will be add to the car table too.
Of course, the other fields such as miles, and year etc.
When search, if people just pick up the make, you pick all the cars with models_id belongs to that make. if people pick up the model, then select the cars with the selecte models_id.
Or you can also design the car table with cars_id, make_id, and model_id, so when search by make only, you just need to select the cars from cars table with that make_id.