Fundamental concepts about Android app development:
For building your first Android app be sure you have your development environment set up. You need to:
1. Download the Android SDK.
2. Install the ADT plugin for Eclipse (if you'll use the Eclipse IDE).
3. Download the latest SDK tools and platforms using the SDK Manager.
To build your app you need to:
1. Chose category of your app like building apps with multimedia, content sharing, graphics and animation, connectivity and cloud, user info and location etc.
2. Create new Android project with the help of the Android SDK.
Read how to build Android apps using the Android SDK click here
.To make downloadable your apps from a play store, you need to upload that app first
Publish your Android apps to the Google Play store. Once you sign up for a developer account, uploading your apps is easy.
Follow the procedure:
1. Click the link to start the procedure https://play.google.com/apps/publish/
2. You need to Accept Developer Agreement and after clicking on "continue to purchase" You have to pay $ 25 (account will valid for lifetime) to purchase the developer app.
3. New windows will pop-up of Google wallet (required credit or debit card for payment) you need to click on "start now" button to Pay Registration Fee.
4.A new window will appear that says "setup Google wallet". After filing the details, click on "Accept and continue" to set up Google wallet (here sign up for a developer account is finished).
5. After this, you need to re-login to the developer account which is created (after the overall process from step 1 to 4 site will automatically show to log in to your account after setting up all the details).
6. After login, you will redirect to developer console where you can see all the apps that are uploaded by your account and you can upload new applications of apk by clicking on "Add new application" button.
In this procedure you just created the developer account to upload your apk apps.
To know more about uploading apps to play store click here