The Primitives, Cone (Surface menu) image\cone.gif command creates a single ruled surface between a circle and a point, with the axis of the cone is always normal to the current CPL:

Primitives, Cone example

Specify any two of the three modifiers to define the cone. Of the three parameters, you can digitise Radius and Height. When digitising, use the cursor to size the radius and height of the cone.

To create a circular surface at the base of the cone, select the Closed option.