Extras is a British sitcom about extras working in television, film, and theatre. The series was co-produced by the BBC and HBO and was created, written, and directed by Ricky Gervais and Stephen Merchant, both of whom also starred in it. Extras follows the lives of Andy Millman (Gervais), his platonic friend Maggie Jacobs (Ashley Jensen), and Andy's substandard agent and part-time retail employee Darren Lamb (Merchant) as Millman muddles through life as an anonymous "background performer" who eventually finds success as a B-level sitcom star. Extras has two series of six episodes each as well as a Christmas Special.
US and UK version differences
There were some subtle changes between the UK and US versions, with references to the names of British celebrities often being changed to American celebrities for the US edition.  In Season 2, episode 1, Keith Chegwin's anti-gay tirade includes the sentence "Men have knobs, women have fannies. Pop knob in fanny. Not up the arse." In British English "fanny" is a euphemism for vagina, while in American English "fanny" is a term for buttocks. A scene was shot, and aired in the US, in which Chegwin says "Men have dicks. Women have vaginas. Pop dick in vagina. Not up the bum."  In Season 2, episode 3, in the scene where Darren Lamb tells Andy Millman about an offer that has come in for Andy to play a supporting role in a film, Lamb mistakenly says the film stars Billie Piper. For the American broadcast, an alternate take was used where Merchant's character says, "How do you fancy three days with Halle Berry?" In each case, Piper and Berry's names are mistaken for the name Harry Potter (actor Daniel Radcliffe guest stars in the episode).  In Season 2, episode 4, a scene featuring UK TV presenter Moira Stuart was completely excised from the US version and a song by Coldplay frontman Chris Martin replaced it; the latter was featured as a deleted scene on the DVD releases.  In the Christmas special the talking "Jade Goody" doll was replaced by a talking "Kramer" doll. (Both dolls parodied incidents where each celebrity said things publicly that were generally seen as racist.) The T-shirt in the studio audience depicting Victoria Wood and Asda is replaced in the US version by a T-shirt depicting Sigourney Weaver and DirectTV. A scene with George Michael was also truncated to remove references to UK celebrities Richard and Judy and Catherine Tate. A scene set in the Carphone Warehouse was edited to remove jokes referring to the long running BBC soap opera EastEnders.

Q: What was the Difference between the UK and Us TV series?
A: references to the names of British celebrities often being changed to American celebrities for the US edition.
What were some other differences between the two
In the Christmas special the talking "Jade Goody" doll was replaced by a talking "Kramer" doll.
In the Christmas special the talking "Jade Goody" doll was replaced by a talking "Kramer" doll.