Hence, a mobile friendly website will rank better on Google Search compared to those that have mobile friendliness issues. This is only true for searches made on a mobile phone though – desktop and tablet search results are not affected.
To check whether your website is mobile friendly, Google has a Mobile-Friendly Testing Page that you can use. You may also check the Google Webmaster Tools.
Mobile friendly websites are also labelled as ‘Mobile Friendly’ on mobile search results. If your site lacks isn't mobile friendly yet, check out Google’s Mobile Guide for tips.
This algorithm update is run in real time so if you make your website mobile friendly by tomorrow, Google should immediately see it and display the ‘Mobile Friendly’ label.
Source: Search Engine Land