The air filter and the fuel filters for your auto are NOT the same. The air filter filters the air going into the intake of the engine for providing clean oxygenated air for combustion of the fuel mixture in the cylinders. The fuel filter filters the *fluid* gasoline before going to the carburetor or injector for introduction into the cylinders for combustion.
Your auto owners' handbook should have recommendations for you to follow in how many miles should be registered on your odometer from the last time each of your filters should be changed out -- depending upon the driving conditions (chances of dirt infiltration of each filter) that have been most prevalent during the times of the mileage traveled.
Your friendly, local, well-recommended service STATION will be glad to talk with you and answer all of your other questions.