One of the most important aspects of your WordPress website is the theme. This controls the look & feel of your site & determines just how professional your website looks.
As with plugins, there are free themes and there are premium themes which you need to pay for. You can also find a free version of many premium versions with restricted features enabling you to try before you buy.
Themes cover a lot more than just the colour of your website. They handle the positioning of plugins and various features. Some themes are also designed for specific use. For example, some themes are designed for an online store. Others might be ideally suited to blog or some for designing a social media community.
Check out the WordPress database of themes and you’re sure to find out a theme suitable for your site.