I’ve tried to make a similar how-to heads up for my team, when they get access. (I have an alt in the beta) At this point, a broad overview is really all that can be made, as the details have changed dramatically over time, and are still under revision/fine tuning.
Atlas expands the world from our bases - islands isolated from each other - to continents made up of multiple territories. Territories range from neutral (no pvp) zones to highly contested high level zones with correspondingly high rewards earned for conquering them and maintaining control. Think of it as a mixture of the strategic elements of Risk or other conquering based board games, with the King of the Hill PVP events, but all the time.
Atlas keeps the aspects of the game we love - flying against other peoples bases - in this case to conquer new territory or defend our own in addition to simply battling each other for fun and profit.
The primary additions of interest to new players are poachers and gold mines. They are equivalent to the daily quests in other games, you attack them for rider gear crafting materials and gold. When flying against those, you fly against an automatically generated ‘Invader’ base that matches your level, and quite frankly, is easy max XP.
The Atlas addition taken in total adds an immense amount of detail to the game, layers on layers of strategy and tactics.
And as Shimo said, inter-team cooperation can play a major role as well. Allying with the right teams can make a huge difference.