Url.Content
is used when you wish to resolve a URL for any file or resource on your site and you would pass it the relative path:
@Url.Content("~/path/file.htm")
Url.Action
is used to resolve an action from a controller such as:
@Url.Action("ActionName", "ControllerName", new { variable = value })
See here for more info:
http://geekswithblogs.net/liammclennan/archive/2008/05/21/122298.aspx – Dead link