You select a nearby drop-point for a (fictional) supply package on a real world map, and run to its location to pick it up!
Airdrop takes place during the first half of Season 2, and the story will progress through one of six missions each time you play, so you won't hear "Mission Completed" after you've reached the drop point until you have heard all of the Airdrop mission stories.
Because the app doesn’t know the exact route you’re going to take when you begin the mission, you may hear the drop-point audio a little bit before or after you arrive at the drop-point.