Templates let you configure all the relevant settings you want pre-applied to documents—page layout, styles, formatting, tabs, boilerplate text, and so on. You can then easily create a new document based on that template.
When you save a document as a template, you can then use that template to create new documents. Those new documents contain all the text (and images, and other content) that the template contains. They also have all the same page layout settings, sections, and styles as the template. Templates can save you a lot of time when you’re creating multiple documents that need to have a consistent layout, format, and some boilerplate text.