A push notification is like a bulk text message that you can send to all the app users. This notification will be delivered to the mobile devices even if your app is not open / active. These messages can be viewed from the app’s push log.

Not yet, but this is on our list of future enhancements. Once a push notification is viewed by the user, does it disappear?

No. Each app has a Push Log, which stores the notifications that the user can share or delete. You can give an easy way to access the Push Log by including it in the footer menu for your app.