The Airglider is one of four upgrades you can unlock via mirage quests. The quest that unlocks the Airglider is the one to the northwest of Pokburr and southwest of Gumquack Hollow.
You can also find the quest via a white dot icon, so look for that. You will need to look for a big white bear-looking creature at this quest location and talk to it.
When you talk to them, you will need to fight a practice fight to complete the quest. Don't worry, It won't matter if you win or lose so just wing it or go all out. You will need to complete the other three mirage quests similarly as well, and each time you do, you will earn what are called Automaton upgrades. That said, when you finish the fight, you will get to unlock the Airglider if you choose it among the choice of upgrades.
Once you got the Airglider, you will be able to use it if you jump and then hold the jump button. After this, your cat mutant will pull the Airglider out, and you will be able to glide with it. We recommend using it as an easy way to get to places until you have a mount or one of the various mechs in the game.