After installing gnuplot it's a good idea to run a simple example to ensure all is working fine.
gnuplot
.gnuplot>
plot sin(x)
If all is well you should see now a sin(x) graphic generated by gnuplot.
Note: if you are on Windows and have not added gnuplot
to your PATH
you' ll need to navigate to the <gnuplot_install_path>\bin
folder. The default location is: C:\Program Files (x86)\gnuplot\bin