A website design typically consists of style sheets, front end modules, page layouts, files and templates, which you can manage in the Contao back end. The theme manager does not change this approach at all, it just adds an option to export and import those resources.
The main difference between themes and front end templates is that a front end template contains a fully preconfigured example website, including an example site structure, articles, content elements and even users and groups. A theme, in contrast, contains only the actual website design and can therefore be imported without losing any existing data.
A theme is a group of style sheets, front end modules and page layouts, which are all stored in the database and automatically recognized by the theme exporter. You will learn more about those elements in the following chapters. A theme typically also includes images and other files from the files directory and optional custom templates from the templates directory. However, those resources are not automatically linked with the theme and therefore have to be added in the theme configuration to be included in the theme export.
To export a theme, simply click on the export button and download the .cto file to your local computer. Although .cto is a proprietary file extension for Contao themes, the file is actually a ZIP archive that can be extracted with every program that handles .zip files. To reimport the theme, upload the .cto file to your Contao installation, open the theme manager and click on "Theme import". You can import multiple themes at once. After the import has been completed, you can assign the page layout(s) of the new theme in the site structure.