Launch/Start Emacs
Emacs can run in GUI mode (graphical user interface), or within a text terminal. [see Emacs: Terminal vs Graphical User Interface]
Launch GUI Emacs, from Terminal
On a text terminal, type:
Linux
# linux. launch gui emacs emacs
# linux. launch gui emacs. and if terminal is killed, won't kill emacs with it nohup emacs &
Mac
# MacOS, launch gui emacs /Applications/Emacs.app/Contents/MacOS/Emacs &

Microsoft Windows
# On Windows, PowerShell. example ~/Downloads/emacs-28.1/bin/runemacs.exe
Run Emacs in Text Terminal
On a text terminal, type:
Linux
# linux. run emacs in text terminal emacs -nw
-nw
is same as --no-window-system
, means run emacs in text terminal.
Mac
# Mac OS X. run emacs in text terminal /Applications/Emacs.app/Contents/MacOS/Emacs -nw
Microsoft Windows
# On Windows, PowerShell. run emacs in text terminal ~/Downloads/emacs-27.1-x86_64/bin/runemacs.exe -nw
Start emacs and open a file
# open a file with emacs emacs fileName