@PrasadAB There could be multiple reasons for it not working.
Considering you're trying on AEM cloud service though the document
you've referred uses older maven archetype, it could be due to that. I
hope you're using latest archetype 23/ 24 in this case.Also, please
check if the model is available under /system/console/status-slingmodels
and you're able to see log statements added for HelloWorldModel.You can
also refer to the below tutorial for setting up sling