Facebook and other social platforms like Twitter, Google+, LinkedIn etc. are taking advantage of social meta tags using OpenGraph protocol. To turn your web pages into graph objects, you need to add basic metadata to your page.
In our themes we provide such option under: Theme Options > Miscellaneous > Meta Tags
WordPress SEO also comes equipped with social features, including the ability to add Facebook Open Graph meta data in WordPress themes. If you already use this SEO plugin then you could enable social meta tags from the plugin instead of our implementation.
Also many third-party plugins provide such functionality. In case you decide to use an external plugin make sure you disable the Meta Tags from Theme Options.
Social platforms provide debug tools to check your meta tags, some of them are shown below