Nothing really happens. It's a charming rural slice-of-life where everyone's nice, but with a dash of the supernatural. Half the cast are witches, although this doesn't mean that they're not also perfectly ordinary girls in a realistically portrayed modern world.
Makoto Kowata is an inexperienced witch. She's also a nice fifteen-year-old girl who's gone to live with her cousins in the country. She has a broomstick, a cat and black robes, but she only gets out the trappings when necessary. She loves nature, she's polite to everyone and she's got no sense of direction, which unusually for anime is never made the subject of jokes. Making fun of that would be too aggressive for this show. Even more surprisingly, another girl (Nao Ishiwatari) is bad at cooking and is forced to cook at school in ep.10... and she succeeds! You'll be waiting in vain for the normally inevitable Cooking Failure.
It's a nice show. Everyone's likeable, although admittedly Kei will occasionally tease people (in his deadpan way) and Makoto's sister Akane is capable of causing modest amounts of trouble because she's happy-go-lucky, likes alcohol and can do difficult magic.
Supernatural things occasionally show up, but they're all nice as well. The ones that can talk will be polite and gentle. The ones that can't will be delightful or intriguing, e.g. the earth fish in ep.12 that like sake and festivals. The flying whale is particularly impressive. The supernatural angle is actually rather nice, giving the show a bit more oomph and making it more than just another slice-of-life anime where nothing happens. It's a door into a magical world. It brings a sense of wonder. Look at the ladybird-chasing in the witch cafe, for instance. It serves no dramatic purpose, but it's still a sweet moment that briefly takes you into an environment where ladybirds can go out on romantic dates.
The cast are pleasant. Makoto is earnest and enthusiastic. Little Chinatsu is the only cast member who shows any kind of reaction to the supernatural and even she gets over her nervousness within a very few episodes. She even decides she'd like to be a witch herself. (Her infinitely relaxed mother is fine with this, but you get the impression that she'd be fine with everything up to and including Godzilla. An alien invasion could be taking place in the garden and she'd be asking if they wanted a cup of tea.) The rest of the cast are, um, well... nice. They're not comedy types or anything, with the possible exception of Akane. It's understated characterisation, which is appropriate for this understated series.
There's no need to watch this show. It's not compelling. A better word would be "comfortable". It's easy to put on another episode, but you wouldn't lose any sleep if you didn't. It's not a comedy, although it can be mildly amusing. Occasionally something would make me laugh (e.g. the shy ghost) or remind me of a Miyazaki film. There aren't even any romantic undertones, either straight or otherwise. (Kei might as well have been another girl for all the difference it would have made. No one shows any interest in anyone else.) This is one of those shows where just looking at the artwork tells you everything you need to know. Do a google image search for "Flying Witch". Looks relaxing and pleasant, doesn't it? You'd like to go and live there. The show's all like that.