So you've fallen behind on the MCU but still plan to watch Ant-Man and the Wasp: Quantumania? Take a seat, as we've got you covered.
The most crucial information for Quantumania came in the Disney+ series Loki, which explained that there are alternate versions of characters from other timelines known as "variants." In the finale, Loki met a man referred to as He Who Remains, who was erasing other timelines to prevent more sinister "variants" of himself from existing.
But after He Who Remains is killed, there are now many timelines and, therefore, many variants of him that pose a threat to the multiverse. The villain of Quantumania, Kang the Conqueror, is one of these variants. At the end of the season, Loki tries to warn Mobius (Owen Wilson) that "countless different versions" of He Who Remains are coming, only to realize he's now in the wrong timeline.
As far as Ant-Man goes, the short version of Scott Lang's (Paul Rudd) story is that he's an ex-convict (who was fired from Baskin-Robbins when his criminal past came to light) and became a superhero after being recruited by Hank Pym (Michael Douglas). In the original film, the villain was Hank's former protégé, Darren Cross (Corey Stoll). Cross was known as the Yellowjacket, and he uses a shrinking suit similar to Ant-Man's. But he was apparently killed after a battle with Scott that ended with Cross shrinking down out of existence in Scott's daughter Cassie's bedroom.
Hank's wife, Janet van Dyne (Michelle Pfeiffer), was missing and presumed dead for 30 years after shrinking so far that she got stuck in the Quantum Realm, a microscopic world beneath ours where time behaves differently. But she was rescued with help from her daughter (and Scott's love interest), Hope van Dyne (Evangeline Lilly).
Scott was also recently stuck in the Quantum Realm for five years after he shrunk down right before Thanos' snap, which turned half the universe to dust in what's known as "the Blip." After getting out, Scott helped the Avengers defeat Thanos by traveling through time and reversing the snap in Avengers: Endgame, but his daughter was now five years older, so he missed a big chunk of her life. Cassie has been recast for Quantumania and is now played by Kathryn Newton.
Also, it's worth remembering that years before Endgame, Scott fought with Captain America against Iron Man as part of a civil war among the Avengers. So if someone mentions Germany, that's where a key battle in this civil war took place.
And that should get you up to speed on the basics for Quantumania, which largely serves to set the stage for two major crossover events: Avengers: The Kang Dynasty, set for 2025, and Avengers: Secret Wars, set for 2026. The road to the next endgame begins now.