You taxi onto the re-arm pad and come to a complete stop.  Your plane will be re-armed and re-fueled.  It will go to the same weapons and fuel you selected when you first launched.  It will not repair any damage.
I find this to be good practice in the offline practice arena.  When you run out of bullets shooting at drones, land the plane, re-arm on the re-arm pad, and take off manually.  This will teach you a lot about how to get your plane to do what you want it to do.