The owner and the club secretary can send one message to everybody. Open the bell and it is at the foot of the list. Up to 280 characters, at most 2 a week. It is the only free text this product sends to your members, which is why the cap is a number rather than a warning.
It reaches everybody on your register, not just the people who have signed in. Anybody with a phone set up for pushes gets it there. Everybody else finds it in the feed. Somebody who has never opened a link at all gets it waiting for them the first time they do. There is no reply channel.