I learned it by making a website that got popular enough to be attacked constantly, and I was basically forced to learn it, haha. But I do enjoy it, it's a lot like the cool computer stories I used to read about as a teenager, where you can see all this connecting activity happening to the server and you have to come up with tricks and tools to prevent each type of weakness in the system as the problems arise in real-time.

If you want to learn the basics, I suggest reading about cloudflare, and all the hundreds of settings that can be set within that commonly-used firewall program. If you understand all the options within cloudflare, you're very well on your way to having a good understanding of cybersecurity. Cloudflare sits in front of the server, and if we get a billion requests it can deal with that and only let the appropriate traffic through. The hard part is coming up with good rules for what is considered "appropriate traffic", which is often unique to every site