How to get help on the shell/terminal

If you are a Windows user, press the keys Windows-R simultaneously to open the Run window, then you can use the help command to get some information on any command, e.g., help taskkill, help dir, or help date. The forward slash (/) is used to execute a command option or perform a switch, the question mark (?) is for the help switch in particular, e.g., ipconfig /?, systeminfo /? or attrib /?  

Other ways to get some help and find solutions to problems in Windows are: Microsoft Support. The Get Help app: Just type Get Help on the taskbar and then type your doubt or problem in the search box. Use Windows Troubleshooters: Settings, System, Troubleshoot, Other troubleshooters.

If you are a macOS or GNU/Linux user:

1. Use the command options -h or -help.

   [username@hostname cwd]$ paccache -h
   paccache v1.5.3
   
   A flexible pacman cache cleaning utility.
   
   Usage: paccache  [options] [targets...]
   
     Operations:
       -d, --dryrun          perform a dry run, only finding candidate packages.
       -m, --move       move candidate packages to "dir".
       -r, --remove          remove candidate packages.
   
     Options:
       --min-atime 
       --min-mtime     keep packages with an atime/mtime that is not older
                             than the time given, even if this means keeping more
                             than specified through the '--keep' option. Accepts
                             arguments according to 'info "Date input formats"',
                             e.g. '30 days ago'.
       -a, --arch      scan for "arch" (default: all architectures).
       [...]
   

2. Sometimes, you don’t know the exact name of a command, then you can make use of tab completion. Just type the beginning of the command and then press tab.
3. If you want a quick way of knowing the purpose and use of a command without going through the whole manual, whatis displays one-line manual page descriptions:

   [username@hostname cwd]$ whatis ps
   ps (1)               - report a snapshot of the current processes.
   [username@hostname cwd]$ whatis surfraw
   surfraw (1)          - a fast unix command line interface to WWW services
   

4. The command man is the general help. Some examples are: man ps, man fdisk.

   When you are reading a man page, remember: / search_string, find matches to “search_string”; n go to the next match; and type q to quit or exit.

5. tldr (aka “Too Long Didn’t Read") are simplified and community-driven man pages with practical examples. Installation: brew install tldr (macOS), sudo pacman -S tldr (Arch), sudo apt install tldr (Ubuntu). Update offline cache of tldr pages: tldr ‐‐update. Use: tldr grep.  
6. You could get access to the best community driven cheat sheets by typing: curl https://cht.sh/ps, curl https://cht.sh/fdisk. You may also want to check: Cheat Sheet.
7. apropos helps you when you don’t remember the exact command but a keyword related to it, e.g. apropos firewall.
8. And last, but not least, cheat allows you to create, edit, and view interactive cheatsheets on the command-line.
   Installation: sudo snap install cheat
   Use: cheat tail
   The first time you launch it, it will ask you two questions: A config file was not found. Would you like to create one now? Y Would you like to download the community cheatsheets? Y.
   To edit a cheatsheet: cheat -e tail.