First you have to Create an AVD(Android virtual Matchine)
you gonna run your application in the Android Emulator.
Before you can launch the emulator, For that you must create an Android Virtual Device (AVD).
An AVD is the system image and device settings used by the emulator.
To create an AVD:
Step1 :- In Eclipse, select Window > AVD Manager.
Step3 :- Click New….
The Create New AVD dialog appears.
Step4 :- Type the name of the AVD, such as “firstAVD”.
Step5 :- Choose a target.
The target is the platform (that is, the version of the Android SDK, such as 2.3.3) you want to run on the emulator.
Step6 :-Click Create AVD.