Before creating any theme in wordpress, you have to understand wordpress file and directory structure that how it will store them and used in building a web pages in our website.
Theme creation in wordpress is very easy and simple process. You can create theme from scratch or download any theme template from wordpress theme template provider sites.
WordPress has been 2003 and best and popular blogging software now a days. Over a last few years, WordPress become most popular CMS for non-blogging websites.