The series starts with our young protagonist Kate Bishop (Hailee Steinfeld) seeing the Chitauri attack on New York. She sees Hawkeye (Clint Barton, played as always by Jeremy Renner), and decides to emulate him. Jump forward a decade and she's intelligent, well trained, and doesn't like her Mom's (Vera Farmiga) new boyfriend Jack (Tony Dalton). They're also very rich, and her Mom runs a security company. At a grand and expensive party, Kate comes to possess - and then wear, in public - Ronin's suit. Which brings her to the attention of a lot of people, including Hawkeye who was Ronin during the Blip (although no one knows that?) and he tries to protect her from the enemies of Ronin, a character he thought he'd killed off.
You need to know the Avengers series, particularly the Blip and the events of "Avengers: Endgame," to understand both the origins of Ronin and Clint's angst about Natasha Romanoff. And "Black Widow," to understand where Yelena (Florence Pugh) is coming from. And then Kingpin (Vincent D'Onofrio) shows up: it would probably help to have seen the "Daredevil" TV series, but I haven't. There's also other stuff in there: a watch that does nothing but is evidently very important, and I found out after I watched the series that Laura Barton (Hawkeye's wife, played by Linda Cardellini) is a former agent of S.H.I.E.L.D., which probably explains her interest in said watch. So I probably missed a lot because I know only the movies.
There's a long-running joke about LARPers in the series: early on, Clint is forced to enter a LARP tournament to recover the Ronin suit, and several of the LARPers resurface later. The initial encounter is insulting to that group of people, but they downgrade that in later episodes. Not, unfortunately, to "respectful," but to "only mildly insulting:" they're presented as "obsessive but competent." I've known LARPers, and to tar all of them with one brush is disingenuous. They're like any other fandom: some are obsessive, some aren't. Some are competent, some aren't. And insulting a fandom that probably has a big overlap with MCU fans may not have been wise. Just saying.
The stakes are lower than the Avengers movies: they make it very clear that while Hawkeye has incredible skills, he's a normal human and he needs medical attention and ice packs after a fight. As does his enthusiastic side kick that he didn't want. They fight criminals in New York. No saving the country, or the world: just ... humans fighting crime. And it kind of felt like Marvel needed to do something like that. It's an origin story too, of course: Kate is becoming a hero, finding out the price and the burdens of the role she wants. And that plays out surprisingly well across six episodes, with it being clear early on how naive she is, and that she has no idea what she's getting into. But Clint mentors her (although he's initially very reluctant to take on the role), and points out just exactly how much her world is going to change.
The resulting product is surprisingly good, and the first MCU TV product I've managed to stick with - possibly because they had the sense to wrap it up in six episodes.