You have a function f(x). To identify the increasing interval and decreasing interval of f(x), you consider that an increasing interval is determined by the values of x in which the value of f(x) increases. For the decreasing interval you focus on the values of x in which the values of f(x) decreases.
You can notice in the given graph:
The increasing interval is (-8 , -4) U (3 , 6)
The decreasing interval is (-4 , -2)
The constant interval is (-2 , 3)
The domain of the function is (-8 , 6)
The previous interval is given by the available values of x
The range of the function is (-4 , 8)
The previos interval is given by the values of f(x) for the values of x in the domain.
The following image is a sketch of the graph with the respective intervals.