Free vs. Premium WordPress Theme

While there are many free themes out there, building a good theme requires time from a developer, so they might charge for it.

Not all themes are made the same way. Always look for themes that are simply well-coded, structured and maintained. You can always look for its reviews, support forums and general ratings for an idea.

For example, a theme may be more minimalistic, making your website more straightforward or more luxury-oriented, making the background black and links in gold colour. 

Themes are not meant to manipulate the actual content of your website, such as words and images. But sometimes, they can add media files to it, so you can have a repository that fits with the aesthetics of your theme.