That depends a lot on her age and what you mean by talk sex.. do you want to have just talk about it, or you want to find out what she likes in sex? or how you can get her to have sex with you. You gotta give more details ..

so while you are adding more details about your questions, here are a few general things to consider. Girls don't like to jump right into a conversation like that, especially for the first time, even if they are dying to talk about it. So key thing to remember is to ease her into it. Ask her if she likes reading romance novels? and hot romance novels like 'Harlequin' series. what are her favorites? what she thinks about the romance and sex in the novels? what kind she found more interesting? why?

If she doesn't like romance novels (that would be crazy for a girl, but still) you can ask her about the movies, but keep in mind that romance novels are very detailed in description of romance and sex scenes that you don't usually find in many movies.

As long as you approach her with openness, honesty and preface the conversations with the words "i love you." I think the way you talk to her is just to talk to her. Make sure you have time for the conversation, make sure you two are alone. Let her know what you want, but also listen to her concerns and be respectful of her reservations. It doesn't do any good to be defensive.