When an Event Notification is created, one or more conversations is created between the SQL Server database engine and a Service. I tend to think of these as “message channels”. When the related event occurs, SQL Server calls the EVENTDATA() function, returning the event information results (as a variable of type XML) to a Service. The Service in turn writes the information to a Queue. A Queue is a FIFO data structure. Conceptually it is similar to a table of rows and columns. You can SELECT from it, but you can’t directly insert or update its rows. You “delete” rows from a Queue via the RECEIVE statement.
Dave has a full example worked out at the link.