If you are a developer or someone looking to design your own website then you may consider using WordPress. It is one of the largest open source website development tools on the market and can be very easy to use. When you first install WordPress it will come with a few standard themes. These themes are often quite basic and may not do everything you need them to. There are many places where you can download free themes but if you are using them for commercial use, be sure to check the license agreement first as some are only free for personal use such as setting up a private blog.
The beauty of WordPress is not only can you install a number of different themes to use you can then adapt these themes and also add Plugins. WordPress Plugins add extra functionality to the site without having to change the whole theme. Some plugins are only compatible with some themes but often you will not struggle to find them.
It is important to check before installing a plugin that it works with your version of WordPress. If not you may need to update your site or find a plugin that is.
Before changing your theme or adding any plugins it is important to back up your site, including the database where all the content is stored. Should anything go wrong you can quickly reinstate the back up.