The problem that you're having now is that you have not set the Page URL in the module parameters. The Page Plugin widget lets you embed a Facebook Page onto your site. If you don't specify one, there will not be anything to display.
Here's the FB documentation for this widget.
Thinking back on it (and it's been awhile since this module has been around), but I believe the JFBCFriends module was for friends that liked URLs on your site. The Page plugin is intended for a Facebook Page, not a page on your site. So my previous suggestion of Page Plugin should be changed to the Like Button. The
If you're intending for to see who likes a specific URL on your website, then you'll have to use the SCSocialWidget module with the "Like Button" widget selected. If you choose to use the URL blank for that widget, the current URL that the module is displayed for will be used. Otherwise, if you specify a specific URL, that URL will be used, regardless of the current URL. The Like Button does also have a setting for displaying friends that have liked the specified URL.
I hope this helps clarify.
-Melissa