If you installed Octave from an installer program, it will likely have
created some icons on your desktop for you to start Octave, either with
the graphical user interface (GUI) or a command line interface (CLI).
You can also typically find Octave in the "Start Menu" or equivalent
of your computer. You can also type octave in a command shell;
as long as you have Octave in your path, it will start.
If you start Octave with the GUI, the central window is the Octave’s
own command-line interface (also called a REPL by other programming languages
for Read-Evaluate-Print-Loop). In this window Octave displays an
initial message and then a prompt like >> or octave:1>
indicating it is ready to accept input. If you have chosen the traditional
command-line interface then the command prompt appears in the same window
that was running a command shell. In either case, you can immediately begin
typing Octave commands.
If you get into trouble, you can usually interrupt Octave by typing Control-C. Doing this will normally return you to Octave’s prompt.
To exit Octave, type quit or exit at the Octave prompt.
On systems that support job control, you can suspend Octave by sending
it a SIGTSTP signal, usually by typing Ctrl-z.