Application Events : Way to Communicate Between Different Lightning Components

SK_ApplicationEventPracticeApp.app

<aura:application extends="force:slds">
    <c:SK_FirstComponent/>    
    <c:SK_SecondComponent/>      
</aura:application>

SK_FirstComponent.cmp

<aura:component >
    <aura:attribute type="String" name="ltngUserInput"/>
    <div style="background-color:#E6E6FA;border-style: solid;margin:5%;padding:2%;">
    	<b>First Component</b>
        <br/>
        <lightning:input value="{!v.ltngUserInput}" label="Enter some value"
                         required="true" placeholder="Enter some value"/>
        <lightning:button variant="brand" label="Send entered value to next component" onclick="{!c.handleClick }" />
    </div>
</aura:component>

SK_FirstComponentController.js

({
	handleClick:function(component, event, helper) {
        console.log("handle click get called.");
		    var appEvent = $A.get("e.c:SK_MessengerEvent");
        appEvent.setParams({"msg":component.get("v.ltngUserInput")}); 
        appEvent.fire(); 
	}
})

SK_MessengerEvent.evt

<aura:event type="APPLICATION" description="Event template" >      
    <aura:attribute name="msg" type="String" access="GLOBAL"/>                           
</aura:event>

SK_SecondComponent.cmp

<aura:component >
	<aura:attribute name="recMsg" type="String" /> 
    <aura:handler action="{!c.handleNotification}" event="c:SK_MessengerEvent" />
    <div style="background-color:grey;border-style: solid;margin:5%;padding:2%;">
        <b>Second component</b>
    	 <br />
    		Passed value from First componet--<b>{!v.recMsg}</b>
    </div>
</aura:component>

SK_SecondComponentController.js

({
	handleNotification:function(component, event, helper) {
        console.log("Event Handled");
        var sentMessage= event.getParam("msg"); 
 		    console.log('******sentMessage by app event:'+sentMessage);
       	component.set("v.recMsg",sentMessage);
	}
})