Place the event bus anywhere on a page.
Place the event receiver on anything that you want to send messages to.
Use the BroadcastMessage action to broadcast events.
How you handle the event is up to you.
Every block with a listener will receive every event, but the common use case is, when you handle the event, check the EventName to see if it’s what you’re waiting for, then if the listening component has an Id (ex. Blocks within a list), check to see if the Id in the message is your block’s Id.
Finally, the data can be used to send anything. For complex structures, you can use serialization.
Additionally, if you put a receiver on a page, you can send messages from deeply nested blocks without having to bubble them up through the ancestor tree. This essentially means that you can have page-level handlers for blocks no matter how deep they are nested.