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.

Here is an example to show the lightning:spinner on click of a button.

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">
    <!--Component Start-->
    <div class="slds-m-around_xx-large">
        <lightning:button label="Click Me" variant="brand" onclick="{!c.handleClick}"/>
        <lightning:spinner aura:id="mySpinner" alternativeText="Processing.." title="Processing.." variant="brand" size="large" class="slds-hide"/>
    </div>
    <!--Component End-->
</aura:component>

Lightning Component JS Controller:

({
    handleClick: function (component, event, helper) {
        helper.showSpinner(component);
        var action = component.get('c.getMessage');
        action.setCallback(this,function(response){
            var state = response.getState();
            if (state === "SUCCESS") {
                helper.hideSpinner(component);
            }
        });
        $A.enqueueAction(action);
    }
})

Lightning Component JS Helper:

({
    showSpinner: function (component, event, helper) {
        var spinner = component.find("mySpinner");
        $A.util.removeClass(spinner, "slds-hide");
    },
    
    hideSpinner: function (component, event, helper) {
        var spinner = component.find("mySpinner");
        $A.util.addClass(spinner, "slds-hide");
    }
})

Output:

We can use lightning:spinner as conditionally, using aura:if or the Lightning Design System utility classes to show or hide the spinner.

The variant attribute changes the appearance of the spinner. If you set variant=”brand”, the spinner matches the Lightning Design System brand color. Setting variant=”inverse” displays a white spinner. The default spinner color is dark blue.