For creating air vehicles, you will need to first have an object you want to use as one.
Once you have the item in your scene, click on it either in the scene window or under the hierarchy.
Under the Inspector window, click on Add Component. Search in the search bar for Plane Vehicle.
This will add the plane vehicle component script to your object, as well as the Plane Physics component and Rigid Body.
Add an animation for the vehicle under the Plane Vehicle component.
Set these accordingly to the item and test it with a play character in the Game window of Unity until you are happy with the outcome.