Full spoilers follow for Avengers: Endgame, so if you don’t want to know what happens in the film, snap your fingers and get out of here now!
So now it can be confirmed. As we long suspected, yes, the Avengers use time travel in order to undo Thanos’ Snap heard round the universe. And while the circumstances of how that time travel play out might be different from what many fans had theorized, the end result is the same: The Mad Titan is defeated and everyone who was lost in the Decimation is returned, albeit after five years of non-existence.
But how exactly does the time travel work in Avengers: Endgame? Basically, it’s super confusing, and it seems like the filmmakers purposely avoid fully explaining it, instead opting to point out how it doesn’t work. That said, let’s put on our Quantum Realm Suit, adjust our time GPS, and time-heist this thing!
Source: IGN.com Explaining the Most Complicated Part of Avengers: Endgame