A theme package contains “template files”. These may contain PHP code, HTML and Template tags. The most common template files are:
- and many others (see more on the WordPress developer page).
Using template files, you can create, for example, a page template.
The default WordPress installation includes a default WordPress Theme. Currently (as of July, 2021), the default theme is Twenty TwentyOne theme (demo). Altogether, WordPress offers eleven themes, starting with TwentyTen which was created in 2010. These themes are free (base on a GPL licence). There are also paid themes available which are very popular among WordPress users. This type of cheap “ready-to-go” solution is not recommended for business websites.
Anyone can build a WordPress theme, but it requires graphic design and coding skills. To create a unique WordPress theme, businesses usually use specialised web design and development agencies.