Mobile:
Go to Messages
Click New Message in top right corner
Type or select Users to include in Message
Type Group Message Name and/or add Image
Click Create in top right corner
Type message in box at bottom of screen
Click Send in bottom right corner
Web:
Go to Messages tab
Click +New Message in top right corner
Type or select Users to include in Message
Click Give a name or image to this group in bottom middle of screen
Type Group Message Name and/or add Image
Click Save
Type message in box at bottom of screen
Click Send in bottom right corner