For a quick example, let's say you wanted a graph of
sin(x). You would then type the following at the gnuplot>
prompt:
plot sin(x)
This will pull up another window with the graph you wanted. If you
made a mistake or want to slightly change what you typed, hit the
UP ARROW. This will pull up what you typed. If you have typed a
couple of lines, you can keep hitting the arrow button. The you can
use the left and right arrow keys to change what you typed. As a quick
example, try changing what you typed to