i want to make my application only in landscape in android

Keep this part of the manifest as it already is. For example, consider the IntroHome activity.

<activity android:name=".IntroHome"
           android:label="@string/app_name"
           android:screenOrientation="landscape"  
           >
</activity>

And for the activity XML, make sure you have the IntroHome activity layout XML only in the layout-land folder. This way, the activity / activities you have will only show the the landscape version of the XML that you have defined.