Hello Venkat,
Before downloading your app, you first need to publish it in the mobile appstores. Here's the guide that shows you how to publish your app to the appstore: https://docs.mendix.com/howto6/publishing-a-mendix-hybrid-mobile-app-in-mobile-app-stores
Regards,
Wilfried
Hi Venkat,
Check the blog and webinar from Mendix about building mobile apps, this should help you to get started.
Blog: https://www.mendix.com/blog/building-mobile-app-mendix/
Webinar: http://ww2.mendix.com/expert-webinar-kick-starting-your-mobile-app-development.html