David Beckham is a British soccer star and the husband of Victoria Beckham ("Posh Spice" of the Spice Girls). His trademark is a goal shot that curves across the pitch and into the net. The soccer equivalent of an unhittable curve ball in baseball. "Bend it like Beckham" means making that type of spectacular shot. Apart from that, and a little shrine to him in the main character's bedroom and a faux-cameo at the very end, the movie has nothing to do with him.
The movie is full of little soccer in-jokes, such as the present that one of the characters' parents give her of a jersey with the number 9 on it (property of the great Mia Hamm, to those in the know), references to "Posh 'n' Becks," the video homage to the WUSA one of the characters plays for a disbelieving friend ("They *have* that??"), lesbian gags, sports-bra gags, and so on.
The story is about a teenage girl in England who idolizes Beckham and wants to be a soccer star. She has a real gift, but the two seemingly insurmountable obstacles she must overcome are the absence of a professional women's league in the UK (hence their fascination with our WUSA), and her parents, who are Indian immigrants set in very old-fashioned ways that do not allow daughters, among other things, to engage in contact sports. The girl's family are portrayed as figures of ironic fun, but with great affection -- think My Big Fat Greek Wedding. The girl loves and respects them enough to go through sitcom hell to conceal her growing soccer stardom from them.