"Talk to your friends on Facebook with this program"
Facebook Messenger para Windows is a chat client with which you can keep in touch with your Facebook friends.
In other words, you can access Facebook chat directly from your desktop using this application without having to log in to the social networking page through your browser. You don't need to be logged in with your user as the chat always keeps you connected and will alert you promptly to new messages.
You can have real-time conversations, each in a different tab and follow them in a linear way just like you do with other chat programs.