Google Play doesn't "assign" random ids to apps. The id is the unique package name of your app, which you choose, so you will know it.
For example:
https://play.google.com/store/apps/details?id=com.facebook.katana
Your app will be:
https://play.google.com/store/apps/details?id=your.package.name
This will be the package you have defined in the manifest.xml
of your app.