Content SEO refers to creating content that helps your web pages to rank high in the search engines. It includes everything to do with the writing and structuring of content on your website. There are three major elements you need to consider to produce content that will make your website rank well: keyword strategy, site structure and copywriting.
Content SEO is important because search engines, such as Google, read your website, so the words you use on your site determine whether or not your site will rank in their results pages. Of course, your website should be well-designed, with a great user interface, and all the technical stuff that makes your site rank in Google should also be covered. But without good quality content, your site does not stand a chance in the search engines.