Every month or two, someone asks me how they should go about learning Unix. The short answer is always "use it" or maybe as much as "use it -- a lot."
But the detailed answer includes a lot of steps and a good amount of commitment to spending time working on the command line. I may have learned some of the most important parts of making my way on the Unix command line the first week that I used it back in the early 80's but I had to spend a lot of time with it before I was really good. And I'm still learning new ways of getting work done 30+ years later. So here is my detailed answer.
The first thing you really need to do if you want to learn how to be productive on the Unix command line is to get access to a system and start working on the command line. One way to do this is to set yourself up with a "live" distribution of Linux -- one that runs from a USB drive or DVD. That way you can both use the Linux desktop and open a terminal window to start trying commands. If you don't mind sacrificing the existing OS on your system, you can install the OS directly on your disk, but using a live version gives you a chance to sample a number of distributions before you pick the one you want to stick with for a while. Knoppix, Mint, Ubuntu, Fedora, Elementary OS and others are easy to boot and use live. Not sure where to start? Some of the distributions that look really good in 2017 are described in CIO.