Follow the steps below when creating a Ruled Surface.
Using the Function:
Select Ruled from the Create>Surfaces submenu.
The Ruled Surface dialogappears, from which you are able to specify how the ruled surface will be created. Configure this dialog as you wish, and select OK.
Depending upon what was selected under Create Ruled Surface Between, you will be prompted to select either two curves or a curve and point between which the surface will be created. Select either two curves, or a curve and a point.
The ruled surface is then created per your specifications.