WordPress Themes are combination of files that work together to create the design and functionality of a WordPress site. Each Theme and their functionality may be different, offering many choices for site owners to instantly change their website look and functionality.Developing a theme for public release isn’t an easy task. There are plenty of elements that are common to blogs that need to be supported in every theme you release. you have a working knowledge of PHP because this is the foundational language of WordPress. So it’s important to know about PHP.