Basically: Wanda and her brother, Pietro/Quicksilver, grew up in Sokovia. Their parents were killed by a bomb made by Stark Industries, the company owned by Tony Stark, aka Iron Man. They became freedom fighters, signed up to have experiments done on them, and other shit. They became super villains because of this and fought the Avengers, then saw the error of their ways and joined the Avengers. Pietro got killed, Wanda went on to do the Avengers thing.
She meets Vision, they get their groove on, she's relatively happy. Thanos shows up in the Infinity Wars movies and kills Vision and half of all life in the universe, including Wanda. Five years later, the Avengers undo what Thanos did (remember when Rambeau wakes up in the hospital? She sort of sees herself being built from dust? That's undoing Thanos' work) Thanos killing everyone is called The Snap, everyone coming back is called The Blip.
Wanda's first act upon coming back was to steal Vision's body, then hijack Westview, NJ and bring him back to life so they could be happy.
That's basically everything leading up to the first episode of the show.
What's interesting to all the comic geeks is that in the most recent episode Wanda brought Pietro back to life. However it is not the Pietro everyone knows, rather it is the Pietro from the Sony Marvel Universe. The SNU has the X-Men, Fantastic Four, and did have Spider-Man, although Spidey is now shared across both universes. The geeks are excited because they see this as having the X-Men and mutants come to the MCU.