Google play is the largest and best Android Appstore which is created and managed by Google .
Google play offers books, apps and movies.
Steps To publish Android App on Google play :
You can create publisher account on https://play.google.com/apps/publish/ link by paying $25.
Once you pay the fee , your publisher account will be activated in 24-48 hours, if not contact to Google Support.
2: Once you your account is activated you can publish any number of Android Application in through your publisher account.
3: Before you publish your app you must have a .apk file signed by private key and you must secure the key because the key is the only way to update your application in future. You can read How to Sign Android App
4: Open https://play.google.com/apps/publish/ and sign in your account, and click on "Add New Application" Button.
5: You will be prompted to Give the Title of the application, Give a goog title and click on Upload apk.
6: Upload your signed .apk file.
7: Click on Store Listing button in left pane and upload all the required things like App Detail, Snapshots, Icon etc.
8: Click on Pricing and Distribution: Select the Countries in which you want to distribute your app.
You can distribute you app free of cast or you can fix a price for your app. To distribute your paid apps you need to create a merchant account. You can create merchant account Here. Google Wallet Merchant Center