your question is a bit vague, the best way to my mins, to learn Linux is to install, use, brake and have to repair your installation, If you are wanting to learn more say to work towards becoming a competent user or a programmer we have lots of tutorials in that section of our forum, [shorter tutorials also on linux-tips.us]
there are also numerous books on learning basic Linux,
there are also accredited courses from the Linux foundation https://training.linuxfoundation.org/resources/free-courses/
Finally, if you're looking at becoming a professional cybersecurity [pen-testing] operative you will need to be fully experienced with Linux, how it works, the terminal and all the main codes [and how they work]