If so then how can we deploy it. Because in my case it is hampering the UI of the team site. It is a simple hello world app. How can we add an app for team site I have created an app catalog site for team site and loaded my custom app. It is throwing some error, "Sorry, apps are turned off. If you know who runs the server, tell them to enable apps".
Seems you did not configure Apps to work in your environment, it's not enough to have the App management service up and running, if you cannot add Apps from the online store, that means you did not configure Apps. You need to configure the subscription settings service application, and do some work with your DNS and in central administration. Refer to the following articles to be able to do so:
http://sharepointchick.com/archive/2012/07/29/setting-up-your-app-domain-for-sharepoint-2013.aspx (Follow option B, it will work 100% for you).
Visual Studio allows developers to deploy/publish Apps for site (site collection) which has been created using Developer Site Template. Recently, I was working for SharePoint 2013 Apps for one of my customer. App was developed using VS 2013 and published on Developer Site Collection (On O365) to test the functionality. However, it was not working (getting an error "sideloading of apps is not enabled…" while publishing app through visual studio) on customers SharePoint 2013 Online Portal as that portal was non-developer site collection.
This will help you: