You can download the source code for your app, for example if you want to continue development on it or customize it. To download your code, first build the app by clicking Test. If the build is successful you will see a notification and it will appear in My Builds.
Click Publish or Download this Build.
In the Publishing Options window, choose Download Source Code. Select or enter the reason you’re downloading at this time, and click Download.
Your source code will download onto your computer, from there you can open and explore it for further development or publication.