Mobile First Indexing is a new Algorithm update which is being rolling out by Google nowadays. Google was experimenting and testing it since long time and after spending lots of time and it is rolling out for the websites.
What is New?
As we know that previous Google was crawling & indexing and the considering the content of desktop version of the website for the ranking system. However sometime it can create an issue for the mobile websites which don’t have the same version as it has for desktop version. In this case mobile user couldn’t find the right results. After this algorithm update Google will use a single ranking system for mobile & desktop devices ranking. It will improve the better result and search experience for mobile searches.
How it will work?
Previous Google was using the desktop version indexing, crawling & Ranking system for desktop & mobile versions of the website but after this update, Google will use a single system (mobile first indexing) for both the version of the website (desktop & Mobile).
How you will notify?
Google will send the message in webmaster central account to the website which is migrating to mobile first indexing. Website owner can see the changes crawl rate by smartphone Google Bot.
If you website is fully responsive and doesn’t have different-different version for desktop and mobile devices and same content is showing for both the version then there is no need to panic. However if you have the different version then you have to make a strong content version of mobile devices as you created for desktop version.