Amplitude is the factor by which a function is stretched vertically. The period of a repeating graph is the width of each repeat. The phase shift is the amount that the graph is moved horizontally.
Amplitude, period and phase shift are used most often for the cosine and sine functions but may be applied to any periodic function. Amplitude is always positive and equals the absolute value of b in the function (b)(sin(x)). Period equals 2pi/k in the function sin(kx). The phase shift can be positive or negative and equals c in the function sin(x-c). For example, in the function 2sin(3x + 1) the amplitude is 2, the period is 2pi/3 and the phase shift is 1.