If you own a web design / programming company or are a freelance web design / programmer, then you should understand the importance of content. Content is king when it comes to websites and marketing as not only can it help persuade the reader to enquire or buy etc, but it can also help get you further up the rankings on Google or other search engines.
As a programmer or a designer, you may not really have much interest in writing copy for sites. Sometimes the client will write the copy and provide it to you to upload, but other times they may ask you to do this.
To be able to write the content to go on their website you may need to interview them to find out a bit more about what they offer. Ideally the person that writes the copy should have a good knowledge of SEO (search Engine Optimisation) to ensure that it is written in such a way that it will improve the SEO on their site. If there is no one within the business who has these skills then it may be time to look at outsourcing the copywriting to someone who is experienced in writing SEO friendly content.