Pasca,
The ability to automatically post a K2 article to Facebook is not in JFBConnect yet. We're planning for that to be in the next major release, in early 2014.
Until that's available, and even when it is, we'd honestly recommend manually posting your content to Facebook. When you manually make the post, you have more control over the time the post goes up, the comment/intro that goes with the post, and other factors. Auto posting does make it easier to get content to your Facebook Page, but manually posting it gives a lot more control over how that content looks on your page.
JFBConnect does have great Open Graph tag support for K2, and should already be setting your title, description and image tags for your K2 (and other Joomla extensions) content.
I hope that helps answer your question,
Alex