In many ways, Facebook Messages work like email, sharing private communications between as few as two contacts. But the Messages app also integrates with Facebook’s chat service, which encourages real-time conversations between larger groups. If you join a chat session associated with other people’s messages, you view all messages in the conversation, even those from before you joined. You can’t add yourself to someone else’s chat session or message thread, but anyone currently in the conversation can add you. Tips Writer Bio
