To set up Show car Types go to the back end > Dashboard > Settings > General Settings > Combine Cars by type: Yes (this setting will combine all cars by type and will only show 1 car result in the Cars section of the booking form). 
Show number of same Type cars: Yes/No - this setting will show a number of Cars you have available at the moment of booking next to Car type in the Car results section.
Show Car type drop down: Yes/No - this option will show all your car types in a drop down on the first step, this settings is optional.

Note: Car type = Car title in car management. All cars of the same type must have the same Title, same number of adult seats and child, infant, booster seats. You can distinguish cars at the back end by Car color (set in Car management) and Car plate number.