lightning:spinner displays an animated spinner image to indicate that a feature is loading. This component can be used when retrieving data or anytime an operation doesn’t immediately complete.

We can control lightning loading spinner using aura:waiting and aura:donewaiting standard events. Both aura:waiting and aura:doneWaiting are application level events.

aura:waiting: Indicates that the app is waiting for a response to a server request.

aura:donewaiting: Indicates that the app is done waiting for a response to a server request.

Example:

Apex Controller:

public class SampleAuraController {
    
    @AuraEnabled
    public static String getMessage() {
        return 'Hello World!!';
    }
}

Lightning Component:

<!--Sample.cmp--> 
<aura:component controller="SampleAuraController" implements="flexipage:availableForAllPageTypes,force:appHostable">
    
    <!--Declare Handlers-->
    <aura:handler event="aura:waiting" action="{!c.handleShowSpinner}"/>
    <aura:handler event="aura:doneWaiting" action="{!c.handleHideSpinner}"/>
    
    <!--Declare Attributes-->
    <aura:attribute name="showSpinner" type="boolean" default="false"/>
    
    <!--Component Start--> 
    <div class="slds-m-around--xx-large">
         <aura:if isTrue="{!v.showSpinner}">
        <lightning:spinner alternativeText="Loading, Please Wait..." title="Loading, Please Wait..." variant="brand" size="large"/>
             </aura:if>
        <lightning:button label="Click Me" variant="brand" onclick="{!c.handleClick}"/>
    </div>
    <!--Component End-->
</aura:component>

Lightning JS Controller:

({
    //Handle Button click 
    handleClick: function (component, event, helper) {
        var action = component.get('c.getMessage');
        action.setCallback(this,function(response){
            var state = response.getState();
            if (state === "SUCCESS") {
                var result = response.getReturnValue();
                console.log('result -' + result)
            }
        });
        $A.enqueueAction(action); 
    },
    
    //Call by aura:waiting event  
    handleShowSpinner: function(component, event, helper) {
        component.set("v.showSpinner", true); 
    },
    
    //Call by aura:doneWaiting event 
    handleHideSpinner : function(component,event,helper){
        component.set("v.showSpinner", false);
    }
})

Output: