For today, I only have a short tip. Some time ago, I discovered this little gem called tldr. This project aims at creating an example-based alternative to man pages. It comprises several hundred short pages containing a short, one-line introduction to the command explained and a bunch of examples.
Of course, man pages are still indispensable. But if you have ever been in a situation when you just wanted to e.g. run GNU find to look for some files but exclude one directory, you know that looking for that in the man page is a PITA. Well, saying just tldr find gives you exactly what you need as one of the examples. Many other utilities are covered, included, but not limited to coreutils. There are pages for many Git commands, the Silver Searcher and its successor ripgrep, HTTPie, tar, screen and tmux, Node.JS, a little utility called x_x I’ve never heard of earlier, youtube-dl, psql and many, many others. You can even say tldr vim or tldr emacs, and, as expected, learn how to quit both! 
(You can also download a huge pdf with all the pages, or install various clients, including several CLI ones and an Emacs one.)
Go to the website of the tldr tool to learn more (also about similar projects!).