Below are some good online references, for learning more about using Linux and for keeping up to date on trends/developments.

Educational

• https://www.linux.com/tutorials
• https://www.tecmint.com/category/linux-commands/
• https://www.lifewire.com/beginners-guide-to-linux-4090233
• http://linuxnewbieguide.org/

Books

The Linux Command Line – free download: http://sourceforge.net/projects/linuxcommand/files/TLCL/16.07/TLCL-16.07.pdf/download

Many more free books to download: itsfoss.com