A template is used to output a module, content element, form or other component and contains HTML and PHP code. In the navigation area “Layout” under “Templates” the files can be created, stored in folders and edited. These adjustments are update proof.
Template changes are not necessary if you only need an additional CSS ID or CSS class. For most Contao components, you can enter them in the “Expert settings” section. The corresponding names are taken from the templates and displayed in the source code.