What did you go through that he should know about? What should I know about?

As a male, not much really happens, other than feeling grumpy as hell pretty much all the time, an undeserved sense of superiority after realizing how logic works, and a fucking intense sex drive. I cannot stress the last part enough, teenage boys are a horny bunch and, thanks to the internet, will probably masturbate multiple times a day. What you should tell him, and hope it enters his brain, is that the more porn he consumes, the less likely he’ll be to feel satisfied with actual sex, which can lead to disappointing relationships later on.

Another couple of comments said to “knock before entering his room”. If you want to “assert authority”, open without knocking and, if you catch him in the act, just nonchalantly tell him to “do it elsewhere and clean up properly” - if anything, teach him to wipe it dry and don’t use water to clean up. He will feel ashamed from being caught, but if you, as his mother, treats it as something natural and expected, hopefully he’ll get the right idea that, yes, that is something to be done in privacy, but not necessarily something to feel ashamed of.

Talk about sex. Tell him that he must wear a condom when he does it and to keep a bottle of lube to help (water based lube only, oils will wreck condoms)

Lastly, if he ever brings a girlfriend home, tell her to only do it with a condom and to not accept any of his possible excuses to not use one.