If you have a website then you need to consider how it is being viewed and used on mobile device. Historically people only ever used a Pc or laptop to view websites but with many of us having smart phones that can access the internet, the need to a mobile friendly website have never been greater. Not only do you need to be able to offer your customers the best experience on your site whilst browsing through a mobile device but search engines such as Google now take this in to account when deciding on where to rank sites in their search engine result pages.
You need to view your site on multiple devices to check how it all fits on the screen, ease of navigating round the site and allowing customers to click links and zoom in and out when needed. If you have video on your site then you should consider if they will enlarge when played or whether they are clicked to link through to Youtube for example.
Analysing your web traffic can allow you to see how many people are viewing your site on a mobile device and what pages they view and also what pages they leave on, this can give you an indication as to any issues with mobile browsing.