To create a curve entity (line, polyline, curve, or combination):
1. Select the Curve-Add Polyline or the Curve Add Curve command.
2. Pick each defining edit point of the curve by clicking the left mouse button. You can override the default curve indicator type by picking using the ‘c’ (curve) or ‘k’ (knuckle) keys. You can also snap to a point by picking the point using the ‘p’ key.
3. After the last defining edit point has been entered, end the command using the right mouse button.
4. Repeat steps 2 and 3 as many times as you wish. The Add Curve command stay active or current until you select another command.
Note1: The default option for the program is to fit or interpolate a NURB curve through the input curve points.
Note2: Snap to an edit point using the ‘p’ key
Snap to a grid point using the ‘g’ key
Snap to a curve with the ‘l’ key
Snap to a surface using the ‘s’ key
To create a curve entity on a surface using the Curve-Add Polyline to Surf or the Curve-Add Curve to Surf commands, you need to follow the same steps as above, but make sure that the pick positions lie on top of a surface in the current view. If more than one surface lies in the pick area, then you need to turn off or hide the surfaces you do not want to attach to. This will create a true parametric curve on the surface.