Google requires all websites to be mobile friendly or responsive, by April 21, 2015. Google will rank your website higher if it is mobile friendly or responsive. Google's change works on a page level not on a domain level, so it might help websites that do not have all pages mobile friendly.
Searches on mobile devices will get better results and pages that are optimized to fit their screen.
If you want to check the status of a page to see if it is mobile friendly, you can use Google Developers tool to evaluate the status. You can also use Google webmaster tools account to get list of mobile usability issues across your site using the Mobile Usability Report.
If you want to check the status of a page to see if it is mobile friendly, you can use Google Developers tool to evaluate the status. You can also use Google webmaster tools account to get list of mobile usability issues across your site using the Mobile Usability Report.