The graphical handles that appear are shown below:
Handle moves the start point of the arc and handle moves the end point. In a full arc, handles and coincide.
Handle moves the centre position of the arc.
Handle edits the radius of the arc.
Where a dimension of an arc is edited, for example the radius, it is displayed on the screen as you drag the handle. How the dimension value increases and decreases depends upon the zoom factor.
In the case of a full arc, when the handle made of handles and is dragged, it splits into two handles. One handle moves with the mouse cursor and the other remains stationary. The full arc turns into a partial arc.
If handles and on a partial arc are dragged so that they coincide, the arc turns into a full arc.
If you are editing a fillet arc, the results of the edits affect the two lines.