With you cursor in the 3D window, press SHIFT+S and select Cursor to Center to put the cursor in the center. This makes sure our new mesh will be created with the same origin as the original.
Now press SHIFT+A and select Mesh->Cylinder.
Step 8
Press T to bring up the tool shelf, and at the bottom under the Add Cylinder options, change Vertices to 12 and Cap Fill Type to Triangle Fan(changes the top and bottom of the cylinder to triangle faces). Also in the Toolshelf under Object Tools, change Shading to Smooth. Press T again to hide the Toolshelf.