Any FREE good sources to learn Linux?

[VertX]

So, Recently, I have tried out Linux, and I have learned a few things, but I want to become advanced with the kernel. So far, I cannot seem to find anything that will teach me about Linux. Either it's a beginner tutorial for Ubuntu, or a dictionary of Linux terms, and the good stuff usually costs money. I feel as though I am stuck, and not sure where to go. Does anyone know any good sources to learn? Thank you.

[Geek-9pm]

... the good stuff usually costs money

What?  The best of Linux is free.
Start with this:
http://linux-training.be/linuxfun.pdf

Linux Fundamentals
Paul Cobbaut
Publication date 2015-05-24 CEST
Abstract
This book is meant to be used in an instructor-led training. For self-study, the intent is to read this book next to a working Linux computer so you can immediately do every subject, practicing each command.
This book is aimed at novice Linux system administrators (and might be interesting and useful for home users that want to know a bit more about their Linux system). However, this bookis not meant as an introduction to Linux desktop applications like text editors, browsers, mail
clients, multimedia or office applications.
...Feel free to contact the author: Paul Cobbaut

In fact, thee is too much real good stuff.   


10 Useful Free Linux eBooks for Newbies and Administrators

Please tell why you need anything else. 

[camerongray]

I'd be inclined to just use it for a while and deliberately make use of the terminal for things.  Once you know the basics you could then move onto trying to install something very bare bones like Arch - Even installing this will teach you a lot and you can then spend time just fiddling about customising things, trying different window managers/desktop environments.etc.  I'm not sure how much of Linux you can just learn by reading about it, it's like programming, you need to be actively doing it rather than just reading.

[VertX]

Both of these replies are really good. The PDF I was sent will be good for me as well.  Thank you guys.