we put the packages that you upload in a "Test App Center". You can activate that on your local system and try out the packages. We do not publish anything to the "real" App Center unless you confirmed that your application works as you expect it to.
Just upload the packages along with the meta files (ini, logo, maybe screenshot and README files) and we will send you an email with instructions how to test the new application.
Further details can be found at docs.univention.de/app-tutorial-4.0.html (specifically chapter 5 and 6).