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.