The gnuplot program creates graphs, plotting points and connecting them with lines and curves, and saves them in a wide variety of printer and plotter formats, such as PostScript. To use gnuplot, you need to learn a small but powerful programming language. Here’s an example of plotting the curve y = x² from x = 1 to 10, which will appear in an X window on your display:

$ gnuplot
gnuplot> plot [1:10] x**2
gnuplot> quit

To do the same, saving the results as a PostScript file:

$ cat myfile
set terminal postscript
plot [1:10] x**2
$ gnuplot < myfile > output.ps

See http://www.gnuplot.info for full details.