Google use its own classification of products, Google Taxonomies.
the Google Taxonomies are help in the ecom system.

To Link your Product Groups to a Google Taxonomy.

Admin > Manage Catalogue > Groups.

1) Click on Google taxonomy, see image.
If nothing is displayed in the pop-up window, see separate article "Download Google Taxonomies".

Link Google taxonomy to Product Group
2) Browse the list, and "Select" closest match from the list

3) Click "Save"

this needs to be done for all product Groups.