People who haven't played the game should have a decent idea of this anyway, but not everyone who has played the game is actually in the beta test. Some of us have played NDA-free public demos.
Of what I've seen, it's similar to Assaults-- you get a quest from a counter NPC, only rather than warping to an instance, you go to an Aetheryte and activate an open-world instanced battle. i.e., everyone is there, but the leve mobs are just for you and your group.
There's also a teleport feature that teleports you to certain Aetheryte (presumably only ones you've been to).
Ok, now we're going to get slash fiction of Wint x Kachi somehere... rule 34 and all...
Never confuse your inference as the listener for an implication of the speaker.
Good games are subjective like good food is subjective. You're not going to seriously tell me that there's not a psychological basis for why pizza is great and lutefisk is revolting. The thing about subjectivity is that, as subjects go, humans actually have a great deal in common.