When you decide on a long-term mobile optimization plan, Google offers three mobile configurations you can choose from.
Responsive design
Responsive web design is the most elegant solution and is recommended by Google.
Briefly, your web pages are on the same URLs for all devices. The HTML stays the same, too. The only thing that changes is the CSS, which alters the rendering of your content depending on the screen size and device type.
Dynamic serving
Another way to implement a mobile-friendly site is dynamic serving.
With dynamic serving, the server responds with different HTML (and CSS) on the same URL depending on which user agent requests the page (mobile, tablet, or desktop).
Separate mobile site
This approach lies in creating a separate mobile-friendly website to show on mobile devices.