Templates - What are templates?

You can copy templates from other wikis, or also easily make them yourself.
For example, suppose you want to start each page with:
Welcome to the Sun Myung Moon archive. Here you find (almost) everything that you want to know about Sun Myung Moon

Make a template page on this website with the title: Template:Welcome.
In the text of this page you write the entire welcoming lines.

In each new page where you want to insert the welcoming text, you write

{{Welcome}}

and the template generates the longer welcoming lines.
In the same way you can add code to the template page.

More info: Mediawiki help for templates