Because of the way the lens on the Canon G series works, you cannot screw an lens or filter directly on.

Instead, these cameras are designed to accept lens adapters that click on.

NOTE:  Be very careful when screwing adapters and lenses on.  If you cross thread them they won't go on properly

Here are 3 examples of what the G10 looks like with an adapter and lens/filter:

G10 Camera with Wide Angle Lens

Steps:

1. Remove  Bezel around lens
2. Install adapter tube
3. Carefully screw on Macro Lens

Canon G10 with Telephoto Lens

Steps:

1. Install adapter tube as above
2. Screw on telephoto adapter ring
3. Screw on telephoto lens

Canon G10 with Filter

Steps:

1. Install adapter as above
2. Screw on filter