1. Choose the degree of the spline in the options tool bar. Supported degrees are 2 (quadratic b-spline) and 3 (cubic b-spline). The higher the degree, the 'smoother' the curve becomes.
   Note that a quadratic b-spline requires by definition at least 3 control points while a cubic b-spline has at least 4 control points.
2. Check the 'Closed' check box in the options tool bar if you want to create a closed spline. Closed splines are continuous closed loops.
3. Specify the control points. After defining the third (for quadratic b-splines) or fourth (for cubic b-splines) control point, a preview will be shown. You can remove the last control point again by clicking the 'Undo' button in the options tool bar.
4. Hit escape or click the right mouse button after setting the last point to confirm the spline shape.
5. You can now create another spline or right-click again to terminate the tool.

Example for two open splines (quadratic and cubic):
Example for two closed, periodic splines (quadratic and cubic):