Publishing at Google Play is very simple and involves the following:
Register for Google Play: Visit and register it at https://play.google.com/. It requires $25 USD to register, and is fairly straightforward and can take a few days until you get the final access.
Uploading APK: Once the registration is over, the users have to log in and upload the APK file using the Upload Application link. Also, they have to upload the required assets, and edit the listing details, the one users will see when they browse the application in store.
Finish up the task by using the publish button.
For more information and help on signing and publishing, refer to following links: