The content on your website refers to the text. Images, buttons, tables etc all tend to fall under code and are not usually “read” by Google. The text on the other hand, is a vital part of getting your website ranking well.
Think about the whole ranking process. Your website has information about your products and services, which you want customers to find and then hopefully buy. It is no accident that certain websites rank higher than others for the same industry. As we know, it is a balance between content, backlinks and technical SEO. The content is a large part of the puzzle.
The text on your website must appeal to consumers, helping them to see why they need your products or services. It is also a good idea to include lots of keywords relating to your products or services, as these are what Google pick up on. The content on your site is how Google can “see” what your site is about, and then rank it accordingly.