For TYPO3, you can use templates in the same way as for all web pages and for more well-known content management systems. There are several kinds of templates already developed that you can use, or you can develop your own template.
It is an important fact that for making an HTML template for your TYPO3 web page, you need to have a basic knowledge of HTML and TYPO3-specific configuration—TypoScript. However, you don't have to know PHP.
TypoScript is a powerful configuration language used in TYPO3. TypoScript isn't a programming language, it is a configuration language that provides output for already-programmed functions. With TypoScript, you can't program new functions.
Most of TypoScript configuration is related to creating templates, but you can also use TypoScript for other configurations. For example, with TypoScript you can configure the column amount in the backend, view of RTE (Rich Text Editor), and available functions, among others...