help <topic>
If <topic> is not specified, a short message is printed about GNUPLOT. After help for the requested topic is given, help for a subtopic may be requested by typing its name, extending the help request. After that subtopic has been printed, you may extend the request again, as before, or go back one level to the previous topic, by simply pressing return without typing anything. Eventually, you will return to the GNUPLOT command line.