A canonical tag is an HTML element. It is used to prevent duplicate content on your site. Use canonical tag on home page. canonical tag is used if you have different URL for same content. use canonical tag on static website manually because in static websites there is less amount of pages. You can use canonical tag on dynamic websites (ecommerce websites, portal websites, news websites, jobs websites) because they have large no of pages. You can also prevent dulicacy from Url Parameter that is available in google webmaster tool.
Syntax for canonical tag:
<link rel="canonical" href="/http://www.abc.com"/>
Syntax for canonical tag:
<link rel="canonical" href="/http://www.abc.com"/>