Also, being pragmatic, I would recommend @Movic start with something like Linux Mint or Elementary OS. Learn bash on them and get familiar with it. Then, start reading Arch Wiki and install Arch Linux based on Wiki rules. It will teach you the most you will need to know for general usage. After that, you can start bash scripting. Learning to write a script in a better way is really beneficial for learning. Plus, you can contribute to Linux if you have that kind of skill. Other than that, just get familiar with the tools you need and love. After a while, you may find yourself more selective in what tools you want in your OS. It is an endless journey as our friend mentioned in the previous post. You may end up being overly selective and end up using something like Gentoo or LFS.Being pragmatic i would ask what hardware do you currently have at your disposal ? I ask this because you can learn the theory of Linux commands but nothing beats actually using them on a PC.