Extension:Boilerplate

The Boilerplate extension loads pre-defined text (from a page named Boilerplate that you create on your MediaWiki site) when a brand new page is created.

Download and Installation
Step 1: Copy-paste this code into a file boilerplate.php and place it in extensions directory.

Step 2: Add the following line to LocalSettings.php:

Step 3: Create a page named Boilerplate on your MediaWiki site. Whatever is included in this Boilerplate page will serve as the default template for any new pages created on your site.

Thats it!