There are too many knowledgeable ...
To such a general request for information on learning linux, are you liable to get very many responses, all well grounded in the particular experience and expectation of the responder.
You might narrow your question by giving us more information about your own experience with linux and what you expect from it.
You can search the forum for this subject and read the many prior threads, naming the several guides and courses online,
However, I too fall to the impulse, temptation.
You can reflect on the criteria below before you post back.