Released in 2010, Facebook Messenger is a free messaging app for iOS and Android smartphones. The application allows users to log in with their existing Facebook accounts and message people that they have connected with on Facebook. The app offers additional features such as voice calls, video calls, unique emojis, and a payment service. Messenger also allows you to view the Facebook profiles of users who message you if the Facebook application is installed.
Facebook Messenger is a separate app then the Facebook app. If you want to use Facebook and Facebook Messenger, you need to install two apps.