The best way to learn Linux is to download a distribution, like Linux Mint. and start working with it. If you don't like learning to swim by diving into the deep end of the pool, another great way to start picking up Linux is to take a class. And, lucky you, beginning August 1st, The Linux Foundation, in conjunction with online education giant edX, is offering a free Introduction to Linux course.
You don't need a Ph. D. to learn Linux and you don't need to have previous Linux experience to enroll. If you know your way around a PC, you're qualified to take the class.
You can audit the course, take it for a certificate, or take and pass the class for an edX personalized Certificate of Achievement. This last option costs $250. This certificate can be used for job applications, promotions or school applications. To earn one, you'll need to be ready to devote 40 to 60 hours to the class.
This course will cover the various tools and techniques commonly used by Linux programmers, system administrators and end users to do day-to-day work in Linux.
After completing the class you should have a good working knowledge of Linux, from both a graphical and shell perspective. You should then be able to easily navigate through any of the major Linux distributions. From here, you should be able to continue your progress as either a user, system administrator or developer. Enjoy!