Facebook has just updated its messaging app. Starting today, Messenger will sort your conversations in tabs instead of having them in a confusing list. At the top of the homescreen, there is a tab called Messages where all one-to-one conversations are listed. The second tab is called Active and you can see if someone is online or when they were last online on Messenger, while the third tab is called Groups - this is the place for all the group chats. On the bottom of the app you will find tabs for the homescreen and calls, positioned left from the camera shutter for Stories....
Source: http://www.gsmarena.com/facebook_messenger_brings_back_messages_as_its_top_feature-news-25114.php