You can easily unblock someone on Facebook Messenger in the "People" preferences section of the app. Here's how to do it.

You can create a "secret conversation" in Messenger by starting a new conversation and tapping the lock icon in the top-right ...

I walk through how I use Facebook Messenger on my iPhone to chat with friends, send photos, and manage settings. I show how to send new messages, create group chats, and share pictures or voice ...