I haven't gone into explicit detail with my son, but we did have a talk about Internet pornography, as I'm so worried that he'll see some and think that is how sex is supposed to be. Our net filters are as strong as they can be, and I closely monitor his Internet usage, but I have no doubt that pretty soon other boys at school will be showing him things on their phones.
I just told him that pornography is not representative of how people have sex in real life, and that the women in pornography are getting no pleasure from the things that are being done to them, and are often probably in quite a lot of pain. I told him that sex should be gentle and loving and about making your partner feel good. I've also spoken to him about trust and respect.