While you search something on Google, the Google page shows 10 pages in the first page and if you click next it ethyl show next 10 pages. It will show the pages based on ranking of the page-the rank of the page will be number of users Visited that particular page.
In Olden days the website developers developing a website for desktop versions only so as day to day technology grows, usage of Palm-mobile devices rapidly increased. In order to access these desktop websites- (supports for desktops and difficult to access in mobiles) in mobile is difficult, loading time is more and data is also waste.
So the developers are trying to develop any website that will support for both desktops as well as mobile. So our work is very simple we can access through mobile and PC's.
But one big question is how to find a website which is mobile friendly-which will take less data to load, less time. The answer for this is , Google provided this feature to know which website is mobile friendly and which is desktop friendly. Naturally every website is desktop friendly so they concentrated on the mobile friendly only.
HOW TO FIND IT:-
If you want to search something you will normally go to the Google page and you will entered whatever you require and you will click Search, after clicking search button it will displays top 10 pages In the first page based on your query ( as I explained top if this page).
After displaying the pages, it will show you left top corner of every page URL- Uniform Resource Locator ( used to find the location of the page), Google's does whether it Is mobile friendly or not. If the page is mobile friendly it will show mobile friendly else it shows nothing.
So if you are a mobile user you can simply saves the time for browsing, data etc.,