Fleur is the superfoxy Triwizard Champion from Beauxbatons. She doesn't get a ton to do in the film, sadly. She's not really very effective in the tournament, as she fails the second and third tasks (with Harry actually sending up a distress call for her in the latter).
She definitely makes her mark on Ron, though. As we know from the book, she's a Veela, which basically means that her beauty is so intense that it turns the men around her to do really strange things.
We see that when Ron decide to ask her out, even though he would never be brave enough to do that normally. As he expects, she says no.
However, she later gives Ron a kiss when she thinks he helped save her sister in the second task. And that kiss about takes Ron out.