How to register, fire and handle a component and application event in Salesforce?

Fire Application Events
Application events follow a traditional publish-subscribe model. An application event is fired from an instance of a component. All components that provide a handler for the event are notified.

Register an Event
A component registers that it may fire an application event by using <aura:registerEvent> in its markup. The nameattribute is required but not used for application events. The name attribute is only relevant for component events. This example uses name="appEvent" but the value isn’t used anywhere.

<aura:registerEvent name="appEvent" type="c:appEvent"/>

Fire an Event
Use $A.get("e.myNamespace:myAppEvent") in JavaScript to get an instance of the myAppEvent event in the myNamespacenamespace.

The syntax to get an instance of an application event is different than the syntax to get a component event, which is cmp.getEvent("evtName").
Use fire() to fire the event.

var appEvent = $A.get("e.c:appEvent");
// Optional: set some data for the event (also known as event shape)
// A parameter’s name must match the name attribute
// of one of the event’s <aura:attribute> tags
//appEvent.setParams({ "myParam" : myValue });
appEvent.fire();

Thanks.