The G cameras havefixed lenses. You can't attach another lens if you can get the first one off.
You can attach tele or wide-angle converters.To do that you need an adapter tube that fits over the lens on the camera. The purpose of the adpter is to provide front threads that converters, filters, hoods and so on can use.
Many prefer this adaper over the plastic one provided by Canon.
http://www.lensmateonline.com/g6.html