Here's a transcript, suitably annotated, of a session with gnuplot. gnuplot can be used interactively, or as a batch-oriented program taking its commands from a file of gnuplot commands.

Invoke gnuplot at the command line in a terminal window by typing

your-machine$ gnuplot

        G N U P L O T
        Unix version 3.7
        patchlevel 0
        last modified Thu Jan 14 19:34:53 BST 1999

        Copyright(C) 1986 - 1993, 1998, 1999
        Thomas Williams, Colin Kelley and many others

        Type `help` to access the on-line reference manual
        The gnuplot FAQ is available from
                <http://www.uni-karlsruhe.de/~ig25/gnuplot-faq/>

        Send comments and requests for help to <info-gnuplot@dartmouth.edu>
        Send bugs, suggestions and mods to <bug-gnuplot@dartmouth.edu>


Terminal type set to 'x11'

At this point, the interpreter is ready for your commands. To plot a graph of, say, y = x³ - 2x + 1, with the view restricted to x-values between 0 and 2, and y-values between -1 and 3, type, at the prompt

gnuplot> plot [0:2][-1:3] x**3-2*x+1

gnuplot will open a graphics window and display a plot of this function.

gnuplot also allows you plot data sets, and to write your graphics output to files in Postscript or LaTeX form. For example, if you have a data set euler.out that you wanted plotted in Postscript form, one way to proceed would be

gnuplot> set terminal postscript
Terminal type set to 'postscript'
Options are 'landscape monochrome "Courier" 14'
gnuplot> set output "euler.ps"
gnuplot> plot [0:10][1:18000] exp(x), "euler.out" with linespoints

gnuplot then builds the graph as the Postscript file euler.ps which you can subsequently view with ghostview, or send to a printer.

To quit gnuplot, merely enter the quit command:

gnuplot> quit
your-machine$

gnuplot provides extensive online help. Just type "help" at the gnuplot prompt (without the quotes, of course) to receive help instructions and a list of topics on which help is available.