What is a discussion?
When you use the "Start a Discussion" option, it posts what you want to say on the feed and posts it in the "Discussions" area.
Anything you want to just 'say' to everyone in the group, should be posted under "Start a Discussion". Think of this as a way to chat about general things.
You can find discussions on the "Discussions" tab on the website, or by tapping "Discussions" along the top navigation on the mobile apps.