The general premise of the game has two players squaring off against one another on a battlefield (this can get up to 3v3 during online matches). On this field are a group of bases and the objective is to A) capture the bases on the map and B) destroy the enemy base. It's a core rule-set that has been used many times before, but in AirMech it's the act of capturing these bases is what makes the concept of the game so compelling, challenging, and a heck of a lot of fun.
Instead of controlling a lot of units on the battlefield, each player can only take control of a single unit: the AirMech which can freely transform between flight and mech modes. In flight-mode the player can pick and up move units around on the battlefled like tanks, turrets, or troops across the battleground. These units can also be given commands like attack or guard. While in flight-mode, the player can also attack other air-based units, but not ground units. That's for the mech-mode which acts as a support class, attacking other enemy ground units and protecting other units on the team.
Base capture is an integral part of success in AirMech. The more bases you capture, the faster your resources will build, and then you'll be able to construct a large scale attack force to overtake the enemy. However, you need smaller units like infantry to capture these bases -- the AirMech is incapable of this feat -- who behave the same way swarms work in League of Legends or Dota (your base will constantly churn out grunts who will proceed towards enemy bases, attempting to capture them). You need to balance not only an attack force, but one that can protect the weakest units while they attempt to capture the bases across the map.
XP can also be earned throughout the battle and used to purchase better units and mechs between matches. You can also purchase different playable characters that have their own special traits, like faster unit movement or better armor as two general examples.