SimDif does not have subpages.
SimDif is designed for each page to have its own tab.
Create one page per topic, one page to answer each general question you reader may have when arriving on your site.
This will help your readers to find more rapidly what they are looking for and increase the chance that they will get in touch.
This kind of organisation also helps Google to better understand the topic and the usefulness of your site. It increases the chances that your site appears in search results.
You can visually group your pages together and add spacers between the groups of tabs using the Move Mode (The hand icon in the top toolbar).