Well, the way I like to learn is: First read a book. And then get the actual thing and play around with it.

This way around you're doing it a bit more methodical. And more effective than just fooling around. But the experience and exercise with the thing itself is also super important. You'll get practical experience and this is often the time you understand why things are a certain way and really start to understand details.

In case of linux: Read the mentioned book. Install a distro without an automatic installer (arch, gentoo, ...). You'll need to read the documentation while doing this. Use Linux daily for a year. Install a webserver, fileserver, ... And if you want to dig down all the way, get through the Linux From Scratch process (but don't start with that, and I don't recommend it either. It's mostly hard work and boring details nobody needs to know.).