You need to add <Intent-filter>
under <activity>
tag in manifest.xml
file like
<activity android:name=".ui.MyActivity" >
<intent-filter>
<action android:name="android.intent.action.SEND" />
<category android:name="android.intent.category.DEFAULT" />
<data android:mimeType="image/*" />
</intent-filter>
<intent-filter>
<action android:name="android.intent.action.SEND" />
<category android:name="android.intent.category.DEFAULT" />
<data android:mimeType="text/plain" />
</intent-filter>
<intent-filter>
<action android:name="android.intent.action.SEND_MULTIPLE" />
<category android:name="android.intent.category.DEFAULT" />
<data android:mimeType="image/*" />
</intent-filter>
</activity>
When another application tries to share any of these things by constructing an intent and passing it to startActivity(), your application will be listed as an option in the intent chooser.
If the user selects your application, the corresponding activity (.ui.MyActivity
in the example above) will be started. It is then up to you to handle the content appropriately within your code and UI.
And go to this for better understanding: http://developer.android.com/training/sharing/receive.html