The domain of a function are all the possible values used as inputs for the function, while the range are all the possible values for the output. In this case we have three points (-1, 3), (-2, -1), (0, -2) and (3,0).
We have the following values as input: {-2, -1, 0, 3}. This is the domain.
We have the following values as output: { -2, -1, 0, 3}. This is the range.
The function is represented by points with no connection between them, this means that the domain is discrete.