When you don't even know where to begin:

• Arch Wiki search
• Docs and wiki for your distro
• StackExchange search
• Sometimes other distro wikis like Gentoo and Debian have some pointers
• Forum search (distros, lemmy, reddit, project issues and discussions)

That should give you one or more possible solutions involving commands. Don't just run them right away. If they're new packages you need to install, you can check some basic package metadata like website URL either via your distros web interface or package manager itself:

pacman -Si packagename  
apt-cache show packagename  

Once installed, hopefully you have man page showing up for man command. If not, they or some other reference docs should be available on the web. Try to find the official resources instead of clickmill tutorial blogs and LLM ramblings like deepwiki. Many but not all commands will give you some usage explanation by passing --help. Any flags/parameters you found in solutions should be explained here. Try to understand the solution/example you were given and what you should expect it to do. Maybe you want to change, add, or remove some arguments for your scenario.

If any files are mentioned, you can open and read them in a text editor. If the command is expected to change anything, or you need to edit config files, you can back those up before you go to town.

Basic cli utilities I use all the time that will help you a lot to be comfortable with: cat less grep diff sudo tee tree head tail curl wget dmesg. If you are ambitious then sed awk jq. If your system uses systemd then systemctl journalctl. No need to remember every single flag but bit by bit you pick up what's relevant for you. And any terminal text editor (nano, (neo)vim, emacs, helix) for sudo edits.

When you want to recall what you did before, you should be able to search your shell history with Ctrl+R. You can put searchable reminders for your future self with comments: brightnessctl s '-10%' # dim monitor decrease screen brightness.