Once you’ve installed the Messenger app, tap to open it on your iPhone.
If you already have the Facebook app on your phone, tap the blue button which says Continue as(Your Name), if the name is correct.
You should see a list of your private messages on Facebook. Tap the Write Message icon in the upper right-hand corner in order to send a new message.
You can send a private message to one person or start a group conversation. Select the names of the friends you would like to include from the drop-down menu.
Write your message in the box where it says Type a message… You can also tap the Photos icon to send a photo from your camera roll, or the Camera icon to take a new photo that you would like to send.
You can even send a voice recording by tapping the Microphone icon.
When you’re finished, tap the button that says Send.