Like so many digital cameras, the G6 needs a conversion lens adapter which provides a 58mm thread for filters and such.
You can see an example at:
Scroll down to the topic titled "Lens"
Cleaning a lens.
The trick is to use a soft cotton cloth.
An old hankerchief is good.
Breath on the lens to create a bit of moisture and wipe it clean with the soft cotton cloth.
Any camera store can sell you a lens cleaning kit if you want to go that route.
My main concern when I purchased the Canon G6 was getting scratches on the lens because it does not have an automatic lens cover. It just comes with a plastic lens cap. When I had my Canon AE-1, I had a protective clear lens over the main lens. Is there something that can go over the Canon G6 lens so it doesn't get scratched? And what do you clean you lens with if it gets a smudge on it?