Many people these days, try to migrate from a non-free Operating System (OS) (like Windows/MAC OS) to a free solution, a free OS like GNU/Linux. Yes, it’s called GNU/Linux not simply Linux acording to the GNU Project.
In the middle of the 80’s GNU Project was created to develop a free UNIX-like OS (The GNU system), unfortunately the GNU kernel was never finished, so the GNU Project adopted the Linux kernel developed by Linus Torvalds. So you can see GNU/Linux as GNU over Linux, GNU OS over the Linux kernel.
GNU/Linux can be found in many flavours called Distributions developed and maintained by different communities. Here you can see an image describing the evolution of different distros. You may also like to take “the test” to find the most suitable one for your personal needs.
Some introductory tutorial for GNU/Linux can be found on guru99 website.