Download Fields - Subform from the RicheyWeb download page.
This page will remain unlinked, as the link may change in the future. Visit http://www.richeyweb.com and use the search feature - search for "Fields - Subform".
In Joomla /administrator, go to the "Extensions" menu, the "Manage" sub-menu, and the "Install" sub-menu.
Select the "Upload Package File" tab
Press the "Choose File" button to browse your system and locate the plugin file you downloaded
Press the "Upload & Install" button
At this point, the extension is installed but not enabled. You can find the plugin by going to the Extensions menu and selecting "Plugins". When in the plugin manager, search for "Fields - Subform".
The only configuration is done outside of Joomla. You must create a filesystem structure to hold your subform packages. The structure must be within the Joomla document root.
On my systems, I create a single folder (named, for example - subforms), and inside I place each subform package directory. Using the twittercard.zip package as an example, the package unzips to a folder named "twittercard". That unzipped folder would be placed inside of the "subforms" folder previously described. The formsource path used to define your subform field would then be: /subforms/twittercard/twittercard.xml
Directory structure of a subform package is as follows:
Your structure may contain additional folders to support fields and media, if necessary.
The packagename.xml file represents the JFormXML subform file.
The packagename.php file represents the template output. If you wish the data to be displayed in the article, it needs only to be echoed, otherwise it can be processed in any way necessary. The twittercard package sends output as meta tags ot the document <head>
Language files follow standard Joomla filesystem structure, using the language string to identify the files. You may add as many language subfolders as necessary.
Please let me know how I can help you to best make use of this plugin.