CMS - content management systems become very popular in last 10 years because of their continual improvement and comfort. They allow you to create website in couple of hours. There are many different CMSs, such as, wordpress, joomla, drupal etc. Many web design companies create their own CMS systems which they are trying to customize for the customers. There are also couple of premium management systems but the open source ones are the BEST.
WordPress has been top leading content management system for couple of years and it comes with many new updates which make it even more powerful and user friendly. There are millions of users of the wordpress and tons of premium wordpress themes available on the online marketplaces. The biggest and the BestWordPress Themes marketplace is most likely to be themeforest.net which contains about 5000 authors and more than 20 000 wordpress templates.
However, you can find many of the FREE wordpress themes around the internet and you might be asking yourself why you should be the premium template when you can just get the free one. Well it depends on your needs. If you are beginner and you just trying to get some ready website where you can practice or just to create simple blog, then go for the FREE one. In case you have intention to start to work with wordpress professionally the premium themes are your best choice. They all come with support of the author and free updates. Updates are important because there are constant improvement and changes in website browsers which can possibly cause a lot of troubles in your web design. Updating the template takes you just couple of minutes and your website is fully back in the game.
You can use wordpress themes also for creating online shops. There are plenty of templates optimized for ecommerce platform and here is little hint for you to make the decision which one is the best for your need! On my website I put together the collection of great auction themes & plugins ... have a look! :)