See the user documentation for this template at Template:Documentation/doc. This template is copied from the English Wikipedia (or other Wikimedia Foundation wiki) template of the same name as this, as found at wp:Template:Documentation.
Purpose

This particular template, copied from the English Wikipedia wiki (or other Wikimedia Foundation wiki), is used to create a shortcut to the documentation subpage for its specific template. It is copied (from en.wp) in accordance with their Creative Commons Attribution-Share Alike license 3.0 (CC-BY-SA 3.0); the same license as used by many other Wikimedia Foundation (WMF) wikis.