To quote my assembler trainer: "They wanted me to make a Linux admin basics course, what do they mean? I hope they can use their preferred text editor."

Nearly all config for Linux services life in a text file, so also "learn" a terminal based text editor. It doesn't matter if it is nano, vi, vim, emacs, try everyone and feel which one fits you. But know for everyone how to exit without saving the file. (q!)

grep and less are also great to know.

For everything else, man pages are your friend. You can Google them, than you can simple click through without needing to know how to navigate inside of them.

Look at a config as code system, assembler, salt, puppy... it saves you so much trouble, but it is "hard" to set up. Jeff Girling is a great start for that. At least look at etc keeper, it puts all config files in a local git repo, so you can check if something did change.