👓 Where do I place my own .sty or .cls files, to make them available to all my .tex files? | TeX StackExchange

Read Where do I place my own .sty or .cls files, to make them available to all my .tex files? (tex.stackexchange.com)
I know how to define a package or a class, but how do I make it available (to myself) at all times? Say I have the package file commonstuff.sty (or myprettyclass.cls), that I want to be able to in...
Missing some files in my installation. I’ll be updating the installation first is the better way to go though….