Theory of sexual development
If you become an object of sexual desire before you come to terms with your own sexuality, you get messed up.
If people are left alone to have nature take its course, they will learn about sex just fine. Cave men figured sex out just fine thanks to hormones and instincts without cultural norms or religious beliefs to complicate the issue. The pituitary gland governs this process quite nicely. Sexual awareness begins when hormones begin doing their thing and suddenly you are aware of your sexual arousal. You recognize the physical characteristics in others that stimulate your arousal, and your hormones compel you to approach bearers of those characteristics seeking sexual contact. Eventually you recognize that others are attracted to you when they respond positively to your advances or initiate advances towards you themselves. And from there your sexual knowledge progresses through increasing experience, Particularly the emotional component of sex.
It is the cultural and media influences upon people in our modern society that can confuse or disrupt this process.