Google have desktop index, but now it starts mobile first indexing. Googlebot crawled website with Desktop user agent and created desktop index based on Desktop site, but after mobile first indexing it will crawl website with mobile user agent and will create mobile index.If you only have desktop site, Google will still crawl it but ranking might affect.

– If you have less content in responsive version of any page of website than desktop version of same page, you should change it and confirm that primary content is same on both Mobile and Desktop.
Content in tabs, accordions will be given more importance in mobile view of site for user experience purposes.

– Now Google Algorithms primarily use site content of mobile version to Rank pages. More to add to understand structure data and show snippets from pages in results it will use primarily mobile version.