Harry sees Ron leaning out "the back window of an old turquoise car, which was parked in midair" (3.2).
Ron's twin elder brothers, Fred and George, are doing the driving.
Ron bursts out: "What's been going on? [...] Why haven't you been answering my letters? I've asked you to stay about twelve times, and then Dad came home and said you'd got an official warning for using magic in front of Muggles —" (3.4).
(Ron's father works for the Ministry of Magic, which is how he knows.)
Ron, Fred, and George have come to take Harry away.
They use the car to drag the bars off Harry's window.
The noise wakes Uncle Vernon, who runs in and tries to catch Harry by the ankle as he goes out the window.
Yet the Weasleys give an extra strong tug and pull Harry into their flying car.
Then they fly off into the night!
Harry explains to Ron all about Dobby.
Fred and George think it's suspicious because "house-elves have got powerful magic of their own, but they can't usually use it without their master's permission" (3.55).
They think "Dobby was sent to stop [Harry] coming back to Hogwarts" (3.55) as a joke.
Harry's mind immediately jumps to Draco Malfoy, his main enemy at school.
Fred and George point out that the Malfoys are an old wizarding family – just the kind of rich, high-status family to have a house-elf.
The Weasleys' plan is to get back to their house before their mother wakes up and their father comes back from work.
They didn't exactly fly to Harry's house with official permission.
Finally, as dawn breaks, Fred, George, Ron, and Harry approach Ottery St. Catchpole, the village where the Weasleys live.
Harry gets his first glimpse of the Weasleys' house: "It looked as though it had once been a large stone pigpen, but extra rooms had been added here and there until it was several stories high and so crooked it looked as though it was held up by magic (which, Harry reminded himself, it probably was)" (3.90).
This is the Burrow.
They try to sneak in, but Mrs. Weasley is too quick for them: "Beds empty! No note! Car gone— could have crashed – out of my mind with worry – did you care?" (3.106).
After scolding her kids for risking their lives, Mrs. Weasley welcomes Harry to the Burrow.
As Harry settles in to breakfast, he sees "a small, red-headed figure in a long nightdress, who appeared in the kitchen, gave a small squeal, and ran out again" (3.121).
This is Ginny Weasley, Ron's younger sister and the youngest Weasley child.
Apparently, she's been spending all summer talking about Harry – she has a crush on him.
After breakfast, Mrs. Weasley sends the boys to help de-gnome the garden.
The gnomes they find in the garden are "small and leathery looking, with a large, knobby, bald head exactly like a potato" (3.141). They are kind of funny-looking and they bite.
To get rid of these gnomes, Ron, Fred, and George teach Harry to grab them by their ankles, swing them in circles, and then hurl them over the hedge.
The idea is to get the gnomes so dizzy that they don't come back again.
Mr. Weasley comes home from his night duty at the Ministry.
He and Mrs. Weasley get into it almost at once. Mrs. Weasley shouts, "Your sons flew that car to Harry's house and back last night! [...] What have you got to say about that, eh?" (3.171).
Mr. Weasley scolds the boys, but he's obviously excited that the car worked.
Ron pulls Harry away from the argument and up to his room.
It's full of magic comic books and toys.
Harry tells Ron honestly, "This is the best house I've ever been in" (3.183).