How to sign APKs

Android Developer page explaining the same thing as below

To test your app on a device you must export an application installer packet (APK). The packet MUST be digitally signed, otherwise your android phone/tablet will not let you install it.

You can use Google's debug Key and Keystore: * The keyring is located at /home/user/.android/debug.keystore * Hint: Go to window → preferences → android → build, you can see the keyring location there * Keystore password is 'android', * Key password is 'android' * Key alias is “androiddebugkey”