After your app is initially built using the  App Wizard, you can now configure your app and design it to your preferences, eg in the   basic settings  or in  app design  and  newsstand design  .

However, changes to the app will not take effect until the app is built again. 

Do you wish to test your app on a tablet or smartphone before going live? In this case, create a preview app and see if the app is up to your requirements. Read   here   how you can build a preview app.

In order to publish an app to an app store you have to build a release version of your app.  See   here   how you can build a release app.