Pages: Is point in custom object with only one control handle possible?
If the handle you are speaking about is the little blue dot used to adjust the roundness of the corners of a rounded rectangle, then yes, there is only one.

(I am assuming the above assumption is true)

To use this handle, simply grab it with the pointer, and drag it. Depending on the object, it will do one of a few things. 

On a rounded rectangle; it will round all the corners to the amount set by the handle.

On a star, it will adjust the sharpness of the points. (The amount of points can be set by the slider that will appear when a star is created.)

On a speech bubble, it will where the 'speech' is originating from.

And on an arrow, it will adjust the shape of the arrowhead, making it sharper, or less sharp.