There are two main types of mobile content. The first one is where content on mobile and desktop are the same. From images to html. Page are made responsive so that they can fit to different screen sizes. Responsive method does not require addition of any content because pages are the same.
Second type is where desktop and mobile content is different. From images to html for sample example.com for desktop and m.example.com for website. This requires designing your website to detect when one is accessing it using a mobile device so that he can be redirected to the mobile pages.
Mobile responsive pages are the most preferred in modern web design.