Redefine control handles for a point on a path
In the Toolbox, click Direct Selection.
Select the path containing the point (or vertex) that you wish to modify.
While holding ALT, click on a node when the cursor looks like one of the following cursors, and then drag away from the node to redefine the control handles.
What it does
Convert point cursor
Makes any sharp corner smooth (if already smooth, changes the angle of the curve as it passes through the clicked point)
Convert segment cursor
Takes a segment and bends it into a curve to pass through the mouse position
Convert tangent cursor
Adjust the selected tangent independently of the other side
Alternatively, you can click a node or a segment of a path to make the tangent handles appear, and then click and drag one of the tangent endpoints when the cursor changes to the move tangent cursor .
For more cursor descriptions, see Pen and direct selection usage.