LibreOffice includes many sample documents and ready-to-use templates. You can access these by choosing File - New - Templates, or press Shift+CommandCtrl+N.
When you open one of the templates, a new document is created based on this template.
Click the Browse online templates button in the dialog to select and download more templates.
You can also use the various wizards (under the File - Wizards menu) to create your own templates, which you can use as a basis for further documents.