There are all kinds of WordPress themes that are available for free when you create a WordPress site. The problem with the free themes is that they are usually incomplete or hey have features that have been deactivated until you decide to buy the premium version of that theme.
People with plenty of knowledge on the use of CSS, HTML and PHP can tweak the free themes and make them even better, but for people with no knowledge, it’s better to just purchase the premium themes to gain full access to the features they offer.