To submit an iOS or Android game to the App Store or Google Play Store, you need to create your package in Distribution mode. To do this, go to the Packaging Settings option in the Packaging menu, and check the Distribution check box.
On iOS, you will need to create a Distribution Certificate and MobileProvision on Apple's developer website. Install the Distribution Certificate the same way as your Development certificate, and name your distribution provision with a "Distro_" prefix, next to your other one (so you would have both Distro_MyProject.mobileprovision and MyProject.mobileprovision).
On Android, you will need to create a key to sign the
.apk file, and give some information to our build tools with a file called
SigningConfig.xml. This file exists in the installed Engine directory (
Engine/Build/Android/Java/). If you edit this file, it will apply to all your projects. However, you can copy this file to your project's
Build/Android/ directory (without the
Java/ subdirectory), and it will be used for just that project. Directions for how to generate the key and fill out the file are found in the file itself.