The completed package should be uploaded to the developer portal within the Packages page. When preparing for upload, make sure that all of your application metadata has been added to the correct locations so that people will find your software easily.
Once the package is uploaded, it will be checked for various errors that could stop it from being released. Should you encounter any warnings, you will need to remove the uploaded build from the portal and fix the issue. Once resolved, you will need to fully re-package, re-sign, and upload the new package for re-testing.