Lore Rundown for dummies:
Aether and Lumine, two siblings that travel between dimensions were fighting evil gods in a war in the past, but they have been banned into a world that has been turned into chaos by the same gods. One sibling arrived I think 500 years earlier and witnessed literally the loss of the other sibling aswell as how the world turned into chaos. Thus sided with the evil of the world to rebuild a new empire and reach godship.
After a placeholder war between different Archons and Gods, the ancient civilization Khaenri'ah got destroyed. It is literally like the Ancient Kingdom in One Piece. Out of this the Abyss Order got created and now the evil sibling is leading this Order to restore Khaenri'ah. On the other side the Archons have built safety havens, cities for mankind and other races to live in peace, but this peace is about to be disrupted by the evil that wants to become god themselves.
There are seven nations in Teyvat and every nation is protected by an Archon. The traveler, the good sibling is about to release all those nations, guarantee the Archons protection, if neccessary convert evil Archons and thus hold back the evil that controls the Abyss Order from making history repeat and have another war between gods, Archons and humans.
So there are several factions in Teyvat:
The Abyss Order that wants to ruin Teyvat and reach God status.
The most evil Archon and probably unredeemable Archon of Shneznaya with their national army called the Fatui, lead by the 11 Harbringers. It seems the Harbringers are redeemable, not like their leader as proven with Tartaglia.
And recently another evil Archon made their move in the recent story arc: Baal the Shogun of Inazuma who seems to be redeemable at the end of the story arc, but that is just speculation.
Very currently Baal seems to have something going on with the Fatui who have also something in common with the Abyss Order and they want to take control over the magical powers of Inazuma where Baal is Shogun.
Baal released a vision hunt decree that hunts vision bearers in Inazuma and literally robs a part of their resolution, memories and will to live. So we are currently participating in a war in Inazuma.
Previously there really was no big tension in Genshin Impact, only major conflict reveals. But Inazuma elevated the story to new levels.
Anyway that is it. There is many possible scum we could look out for flavourwise. But yeah that is it.