At the end of Loki's first season, Sylvie used He Who Remains' TemPad to send her fellow Variant away. With that, she was able to finally take her revenge on the TVA's founder, driving a dagger through his chest (she'd been on the run from the TVA ever since her timeline was pruned).
After killing the ancient Kang Variant, the Sacred Timeline started branching, leading to the apparent rebirth of the Multiverse. As for Loki, he found himself back in the TVA, but neither Mobius nor Hunter B-15 recognised him. Shocked, he looked around to see this version of the TVA was openly ruled over by Kang.
The general assumption since then has been that Loki was inadvertently sent to a different reality, but the truth is finally revealed in today's season 2 premiere.
When the episode begins, Loki is on the run from his former allies but begins time slipping; we then learn the God of Mischief was actually sent to the past and that He Who Remains' likeness was indeed once used in place of the fictional Time-Keepers. The present-day TVA agents, however, have no memory of this time.
As Loki continues unwillingly jumping between the past, present, and future, the present-day Mobius takes him to Ouroboros/O.B., the TVA's tech expert. As Loki continues to slip between the past and present, he's able to convince the past O.B. to create the device which can one day save him.
However, we learn that the TVA's Temporal Loom is struggling to handle all those divergent timelines and the only way for Loki to avoid being torn apart is to use an extractor which can pull him out of the time stream. However, he'll have to prune himself just as Mobius hits the switch.
Things don't go exactly to plan and, in the future, a ringing phone draws Loki to an elevator where he sees Sylvie right as he's pruned (presumably by his female Variant). On the plus side, he's successfully extracted and lives to fight another day.
The stakes remain high, though, as the Temporal Loom - where raw time is refined into the physical timeline - is still overloading. If something isn't done, time itself will be destroyed and all those new branches are at serious risk. Then, there's the small issue of a TVA agent called Dox.
After Loki reveals the truth about the TVA, she assembles an army of TVA agents to track down Sylvie, the Variant who caused this problem in the first place. Oh, and let's not forget the small issue of all those Kang Variants and the possibility of a new Multiversal War...