No Stupid Questions

First things first, I'd suggest looking into Big Brothers, Big Sisters if you're in America. I've been a part of their program and it's a great organization dedicated to helping kids exactly like this

OK, onto real advice: it sounds like you're a woman and one of the things you need to address early with young men is respect. He will become significantly stronger than you very soon. He will have a ton of hormones pumping through his body. He is going to become dangerous to himself and others. He will be curious about how strong he is. You have to make sure he explores that safety. This is something all men go through and it's important to have a good foundation or he can start spiraling down bad paths. You need to police his internet usage, his friends, and his role models or he could very easily start sliding into anti-women and abusive views

If he's not enrolled in any sort of physical activity I would encourage you to find one. He's going to have basically unlimited energy and channeling that into sports is usually better than the alternatives. That's also tricky because you need to pay attention to the leadership of those activities to ensure that they are good influences

Now the fun stuff: he is going to be hungry for the next 5 years. If you haven't grown up with boys it's hard to understand but he can eat 6000 calories in a day and barely notice. My family used to order 2 pizzas when I was a teen, I would eat an entire one and they would eat the other. I'm not exaggerating when I say my average food in a day was a full continental breakfast, 2 deli sandwiches, chips, a dessert and a soda for lunch, an after school snack (usually leftovers), a large dinner, and dessert. I'm not a fat guy, nor was I in school. You will likely think at some point "he can't possibly be eating that much food" and I assure you that he can

Ultimately what is important is that you have to build a good moral foundation for him. You will lose the ability to control him and when that happens all of the work you've done raising him will reflect in the way he acts

For real, go to a library and ask a librarian for help.

They'll have various books aimed at different levels of maturity and reading levels. Get a book, read it yourself, then ask him to read it and talk about what you learned.

In this day and age with the internet, I doubt there's much he doesn't know about in terms of how it works.

I would pull up statistics on stds and on the cost of raising a kid. Explain to him that almost 1 in 8 people have herpes and it never goes away, and how teen pregnancy really can fuck up future opportunities.

Here's what I wish people had explained to me when I was approximately your son's age and which should cover most of what he's going through:

(I am assuming your son is heterosexual. If he is not, then you have to change this somewhat, but I can't help you with that very much because I'm heterosexual myself.)

You probably noticed that for a few years now, when you look at or think of girls, your penis gets hard and much bigger; this is because you started puberty. That is called an erection and is a completely normal thing to happen; it's your body telling you that it would like you to have sex with that girl. Erections will immediately go away when you ejaculate, which is a completely normal and very pleasurable thing to do. You can ejaculate without having sex with anyone by masturbating, that is, by rubbing your penis against your hands or some other object. It helps to think of beautiful girls when doing that. I have no problem at all with you doing this and you will never get in trouble for doing it or asking anyone any questions about it, but I insist that you do it when no one is watching, preferably in your own room.

In my region this is handled really well by schools. Parents don't need to worry about anything. Don't they do that in your region?

Have you reached out to his coaches/PE teachers at school?