The function given is a graph of a trigonometric function.
The amplitude is the distance between the peak and the midline of the wavelengths. The midline of this graph is at -4 while the peak is at -2 and -6. The amplitude therefore, is the distance between -4 ans -2 (or -4 and -6.
The distance in absolute value is 2. The amplitude therefore is 2.
The period is the distance covered by one revolution. The period in this graph