a normal sine curve has amplitude 1 and period 2pi, which means it has a high and low of 1 and -1 and completes a full cycle along the x axis from 0 to 2pi
in this case, the 3 in front changes the amplitude to 3, therefore it has a high and low of 3 and -3
then the 3 by the x changes the period by 2pi/3 which means it completes 3 cycles from 0 to 2pi on the x axis instead of one.
if using a graphing calculator, it must be in radians