In the Page Editor, you will make changes not only to the main content on your site, but also to the "Modules" to be included on each page. When you select a module, you will be prompted with any categories associated with that module. Categories are used to help you further manage your content. On a page which is about Adult Ministry, you may not want to show news, Bible studies, etc. that are associated with youth. By assigning only the Adult category to the news module on this page, your news will be displayed accordingly.