Name the curve in Curve name field if you want a custom name.
Click the pick surface button and select each edge that you would like to extract with the mouse. (Since the screen is often crowded with surfaces, the Select dialog box will often be displayed for you to help select the proper surface.)
The location of the pick is used to select a surface AND extract a trimming edge. Click the Use Next Edge of Surface if you picked the correct surface, but the wrong edge.
Continue selecting edges in order until you have selected all edges.
Use the arrow keys to reorder the edges if necessary.
If the edges are in the correct order, but the endpoints are matched up incorrectly, select the surface name in the table and click the reverse arrow.
Click Connect Start and End Points if you want the curve to be automatically closed.
Click Project to UCS to have the curve automatically projected to the 2D XY plane of the UCS.
If a hollow blue square is displayed at the intersection of two edges, then the edges have not quite matched up. You can correct this by either selecting the missing edge that will connect the endpoints, or if it is just an issue of floating point error, increase the tolerance parameter.
Click Finish (or OK if you’re not using the wizard) to create the curve.