Hold and legend function:
hold: is a toggle which freezes the present graph in the figure window, so that the new plots will be superimposed on the present one. Just hold by itself is a toggle, therefore calling this function once turns hold on, and then next time turns it off. Alternatively, the commands contain on and hold off which can also be used.
legend shows strings passed to it in a legend box in the figure window, in order of the plots in the figure window.