Easy way..
1 .Go here
http://developer.android.com/sdk/index.html
2. Download the bundle for your OS platform
3. Start programing through the eclipse editor with an existing template or do the “Hello world” tutorial.
4. Current Java version (jdk) which also includes (jre) may come in useful.
5. Have fun

Run it first on the emulator within eclipse for the required android version ie 2.2, 2.3, 4.1. etc then connect you phone to your computer, run it again and eclipse will run it on your phone. All my phones are rooted, but for this is not required. Don’t forget to check “Allow unknown” in your phone settings.

You can get eclipse from this website:

http://www.eclipse.org/downloads/

Just choose your OS. Then you have to download the android plugin for eclipse. This is how:

http://developer.android.com/sdk/installing/installing-adt.html

Then just write your app in Java, test, debug, over and over again and you’re done Smile (WARNING: This might be a tiny oversimplification of the process).

You can also download the whole bundle at once here:

http://developer.android.com/sdk/index.html

Use eclipse.And android SDK.It’s simple as it is.Can use Java and C++.But if you use java you can find lot of online materials and can use android sdk(software development kit).If your application needs more efficiency can use c++.If you use c++ you should use NDK(Native Development Kit)