I’m sure you’ve noticed that Facebook automatically includes a picture, title and description when you include a website URL in your status update.  Facebook gets that information from your website’s metadata.  If you’re using WordPress, you can control the meta description on individual pages using a plugin like Yoast’s WordPress SEO.  Once you’ve updated your website, you can get a preview of how that will look in Facebook using their debugger tool at https://developers.facebook.com/tools/debug.

Have fun!