I am also trying to learn linux. I have been interested in Linux for years, and have always found it a difficult subject to learn on my own. While there exists a vocal minority who have learned Linux on their own and through the available documentation and resources, most people who attempt to learn Linux on their own ended up dejected and frustrated. As evidence, the most successful distros like Ubuntu are popular because they attempt to mimic the Microsoft Windows experience. Many people are migrating to Linux, but they are not learning the system.
There is good and bad news. The bad news first; it provides context. The bad news is that the Linux culture is a tech savy, boot-strap kind of culture. The first Linux devotees were already experienced techies in their own right. They were willing to help others along, but they were not willing and in many cases completely unable to teach a newbie how to run a computer much less an operating system. In the bad old days, newbies often received helpful messages like "RTFM" in response to their more basic questions. Today, most Linux devotees who have, in fact, mastered Linux are still experienced and accomplished techies. The profile of a Linux devotee has expanded, but the Humanities remain under represented among the more accomplished Linux users. Most people who have mastered Linux are busy, hard working persons with plenty to do. They are willing to offer their to time to help new comers, but they can't afford and often unable to provide the documentation and guidance that a true newbie actually needs to find their way into a Linux distribution.
The good news; there is hope. First, the Linux community is expanding and many new persons are emerging who have the technical skills to understand and to teach. Second, hardware is changing. Better and better books are available everyday. The bad old days are mostly gone, and most forum posts will be answered in timely and courteous manner.
People in the Linux community have always been genuinely willing to help, but the changes in hardware and the population of the Linux community are producing a new environment with enormous potential.
If you want to learn Linux, you must first understand the scope of the task. Learning Linux is not like learning a software package with a graphical interface. Learning Linux means learning computer science. A Linux installation is designed and intended to give the user the ability to manage their computer and software from the user interface to the hardware by directly manipulating the operating system. Hoo ah! Learning Linux is not a trivial task.
Begin at the beginning. (No, The Debian System Administrator's Handbook is not the beginning.) The beginning is an introduction to computer science. No, I have not been able to find a textbook introduction to computer science based on Linux much less the Rpi. The Linux community needs one, and I hope that someone is working on one, but to my knowledge, it ain't here yet.
I can make some recommendations based on my own limited experience and severely limited financial resources. First, use the Rpi as your learning aparatus. Don't buy a monitor, keyboard, etc. Connect to your Rpi through a Chromebook. The cost of the Chromebook is comparable to the cost of a monitor, etc., and you will be able to use the Chromebook to effectively navigate the web. You can connect to your Rpi to Chromebook using ssh and vnc. (ssh and vnc are two fairly easy tools that allow the user to network computers. The tutorials here are sufficient.) For books, I recommend "No Starch Press". The specific titles that I am using are "How Linux Works", "The Linux Command Line" and "Practical Vim: Edit Text at the Speed of Thought". You will eventually need to learn at least two programming languages. Nobody learns Linux without learning C scripting. You'll probably want something less tumor inducing. I expect to go with Python. Many people learn Java and, the hardcore master C.
Other people will tell you that I am exaggerating. I was told the same and wasted years looking for the "simple" or "easy" way to learn. It is not easy to learn Linux. I believe that it is worth while. I expect the task to become more straight forward in the future. If nobody else writes the d**n intro to comp sci with Linux, I will - eventually. Best of Luck. Let me know if you find any good resources.