The function object has two modes: "linear" and "curve". When in the linear mode, the output will output value pairs that represent the time and target value for each of the points in the function display. Typically, this output is sent to a line~ object, which can be used to drive almost any object at audio rate.
When in curve mode - either set in the inspector or using the mode message - the function object produces output consistent with the values required by the curve~ object - value triplets that include delta time, target value and curve value. The curve value ranges from -1.0 through 1.0, with positive values producing a logarithmic curve, and negative values producing an exponential curve:
When function is in curve mode, you can directly change the curvature of any line segment by option-clicking on the segment, then dragging vertically.
(To learn more about logarithmic and exponential curves, you can check out this site.)