When smartphones first started to be used for browsing the web, more and more companies quickly caught on that they needed to ensure their website was compatible. They often created a version of the website to be viewed on mobile devices or tablets. The issue with many of these sites is that the mobile version often seemed to be very stripped back and looked quite plain. Although this is good in a way allowing for easy navigation across a smaller screen, it also meant that some of the advertising that companies have got on their sites wasn’t been seen by an increasing number of people who browsed using their mobile device.
Ideally, you want to have a mobile version of your site that looks likes your desktop version (using same colourways, logos etc, but is easier to use. This may mean changing the navigation to buttons along the side rather than having to zoom in and out to navigate different parts of the site.
Make sure that it is easy for someone to swap between the desktop version and mobile version as someone who is used to looking at your site on a desktop may prefer to use that version when on their phone too.