The story is that he is Andy, a movie extra who wants to be an actor, and the action is set around the productions he's in. His best friend Maggie is also an extra, a Scottish girl who seems a little dim at first, but she grows on you. Each episode has a real movie star in it, who play themselves, or rather play versions of themselves that are in their own way as pathetic and ridiculous as Andy and Maggie.
The thing I liked about it is the way Gervais makes comedy of embarrassment work. All the characters make asses of themselves, but in mostly subtle ways. The funniest episode is the third one with Kate Winslet, and features a girl with cerebral palsy, who gives Andy ample opportunity to be singularly offensive. I won't go into the thing with Kate Winslet and Maggie, so as not to spoil it -- it's a joke that takes the full half hour to pay off, and it's hilarious.
The other thing to like about Extras (and Ricky Gervais) is that the set of six episodes work as a single set piece. They're going to do more, but as Gervais did with "The Office" it's a series that runs a dramatic course and ends. You don't have an open-ended thing that keeps running until it jumps the shark.
Again it goes to show that the Brits do better TV than our broadcast networks do. HBO of course has done some cool stuff, and stuff like "Weeds" -- which I'm downloading now -- is pretty OK, but "Extras" -- like "Sugar Rush" -- would never get made in the US, without being ruined, somehow. My brother Ian and his wife Tessa are out in LA trying to pitch series ideas, and I know it's no bed of roses.