Category configuration on default level.
Products are categorized in Google Shopping according to the Google product taxonomy. While Google cannot guarantee that a product will show in a particular category, you can increase the chances of your products being included in the most relevant categories by sending them highly structured information for your items.
Click here to read more about the Google product Taxonomy including the different categories.
Category configuration on category level
To increase the applicability of the categories in the Google shopping feed, you can use the Google shopping product taxonomy and configure them in the category management product tab. Click here to read more about the Google product Taxonomy including the different categories.