I don't know how to do it, but an example is in the video below
http://s237.photobucket.com/albums/ff15 ... linder.flv

I'm trying to make some models for my map, but need to know how to do this first. I looked for it, I just don't know what this tool is called.

This is what I did in the video:
Press the U key for raycast polygon selection
Select the polygons on the end of the cylinder
Press ctrl+d to duplicate the selected polygons
Press X key and scaled the duplicated polygons in X and Y axis
Press ctrl+d again to duplicate the selected polygons once more
pressed V key and translated in -Z axis

Press F1 and have a look through the XSI docs for more info.

Hope this helps

yeah I guess it was duplicate I didn't know