At least that is the unwritten rule. There will be a few shy or boastful words, some dirty jokes, but no more. It makes 'sex' and sexuality feel a bit dirty, even wrong or something that should be hidden. As a result, we keep our problems and insecurities to ourself and don't really fix them. It might feel like you are the only one with a particular problem, since no-one speaks about it.
Besides that, I think we should be learnt so much more about our bodies than we are now. What does being pregnant and having a baby actually feel like? We only hear the pretty stories; "it'll hurt, but when you hold your child everything will be forgotten and everything will be fairytale-fine". How do you actually take care of that down there, vagina or penis? How do you keep it healthy? How do you love it in a healthy way?
And then sexual intercourse… It is something that has a deep psychological and chemical impact, but we don't speak about the 'details'; the problems and just overall the topics we encounter there. Why don't we? I'm sure there are many (mostly cultural) reasons, but I think we should talk more.
I recommend snooping around on YouTube a bit too. (Yes, you heard it; youtube.) There is a lot of information to be found on there. For instance I can recommend the educational video's by Makeda Voletta. She researches and teaches on the feminine sexuality and gives information that should have been taught all young girls, in my opinion.
Now, let's talk about sex.