Mobile-first Indexing: What is it? How it Works? and What to do next?

Earlier this week, Google began sending mobile-first indexing notices to webmasters of the websites who are using search console. Previously, mostly the sites that were not mobile-friendly were first moved but now, even mobile-friendly sites are being moved. So, now that Google has officially rolled out mobile-first indexing, I am going to explain what is mobile-first indexing, how it works and what should be the next steps to be followed as the best practices. What is mobile-first indexing? Before I try to explain about mobile-first indexing, let us look at the description provided by Google when the same was announced:  “To recap, our crawling, indexing, and ranking systems have typically used the desktop version of a page's content, which may cause issues for mobile searchers when that version is vastly different from the mobile version. Mobile-first indexing means that we'll use the mobile version of the page for indexing and ranking, to better help our – primarily mobile – …