This answer from davecole:
To create a simple cone you need to start off by drawing a circle with the diameter of one end of the cone. Below I drew the bottom of the cone.
Pull (P) the Circle to the height of the cone required
With the Pull tool selected, Select the edge of the diameter to be reduced.
A Single Click on the diameter will also bring up the quick menu as shown below.
Select the "Pivot Edge" tool which will change the pull arrow to show two arrows (radial and axial).
Select the radial arrow and pull to the new diameter