Problem in Android Studio

After installing Android Studio.MainActivity.kt is not present.what to do?

You can add it explicitly. Right click on package name and new -> empty activity and name it as main activity. Also make sure to make activity as launcher activity.

<activity
    android:name=".MainActivity"
    android:label="@string/app_name" >
    <intent-filter>
        <action android:name="android.intent.action.MAIN" />
        <category android:name="android.intent.category.LAUNCHER" />
    </intent-filter>
</activity>