when you submit your app, you will recieve mail from MS.
open it in your WP8 device and press the link ,
example from the email I recieved: " Before you install your Windows Phone App Studio applications you must install this certificate on your phone (click here). "
it will download certificate to your device that will let you download, install and run your application without submitting it to the store.
example from the email I received :" Congratulations! Your application My Shopping List has been successfully generated. Please, click the link below to check the result:"
good luck....I was really disappointed from this environment, very limited capabilities (for now I hope.....).
"touchDevelop" environment is much better and let you also export your app.