Android Market is a hosted service that makes it easy for users to find and download Android applications to their Android-powered devices, and makes it easy for developers to publish their applications to Android users.
To publish your application on Android Market, you first need to register with the service using your Google account and agree to the terms of service. Once you are registered, you can upload your application to the service whenever you want, as many times as you want, and then publish it when you are ready. Once published, users can see your application, download it, and rate it using the Market application installed on their Android-powered devices.
To register as an Android Market developer and get started with publishing, visit the Android Market: http://market.android.com/publish .
If you plan to publish your application on Android Market, you must make sure that it meets the requirements listed below, which are enforced by the Market server when you upload the application.
Note: There are many third market such as Amazon. You could market the showcase APP on those market like Google Market.