You can move a control point by dragging it with the mouse, add a new one by clicking the mouse, and delete one by holding down the Shift key while clicking on it.
Each four control points defines a cubic curve. This curve interpolates the first and last control points and approximates the other two. Unlike a natural cubic spline or a B spline, adjacent Beziers do not join together smoothly (You need to add three control points to the curve above to see another curve added). By adjusting the control points it is possible to get the Beziers to join without corners.