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