Noob here. I'm beginning to learn but I'm confused about the different client/server side of websites

I'm completely new to programming. I started off learning HTML/CSS, on to Python, now Javascript. I've forgotten a lot of the Python so I will have to redo the course. I'm also learning all this on Codecademy by the way. My question here is, and I hope I came to the correct place, what's this different "sides" of a website? For example, I learned Python thinking that it'd help me make a website like Youtube (Codecademy said Youtube used Python!), with beginner's naiveté, I realized I needed to learn Javascript to make sites interactive first and a LOT more stuff I don't know.

I just need someone to explain to me, for a "website", if you can call it that, like Facebook or Youtube, what are needed to create them? I've progressed far enough to now know that HTML/CSS and some Python is far from all you'd need to create Youtube (I actually thought that at first...)

I mean all the deep down stuff - like HTML/CSS/JS, etc for the part people see as well as the part people DON'T see, and all the databases, servers, etc.

I've progressed far enough to know that companies like Facebook/Google/Youtube aren't called "websites" for a reason, because they're not static webpages whose assets are a bunch of programmers and some computers, but an actual dynamic company like WalMart with assets like huge storages/server space.

Enlighten a newbie. Thanks in advance.