Templates are used to add recurring messages to pages consistently, to create navigational boxes, and to provide cross-language portability of texts. The content of a template can be added to a page by typing {{templatename}}. The “Template:” prefix doesn't need to be included. The first character (only) is not case-sensitive, so {{delete}} and {{Delete}} are the same.
In the gallery namespace (also referred to as mainspace, the main namespace, or the article namespace in Wikipedia), templates exist only to help readers. These can include navigation aids and warnings that content is substandard. Templates that provide information only of service to editors belong on a gallery’s talk page.
If you wish to experiment with templates, you may do so in the Sandbox.
See also: w:Help:Template.