menu directory is missing

You can create a menu dir in the res/ folder. Right click on res in the project view in Android Studio and click new -> "Android Resource Directory". Then select menu under "Resource Type". You can then add a file to that new res/menu directory that contains your menu items like this (res/menu/main_menu.xml)

<menu xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto">
    <item
        android:id="@+id/action"
        android:title="@string/action"
        app:showAsAction="always" />
</menu>

And get sure to override the onCreateOptionsMenu(Menu menu) in the MainActivity class like this:

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    MenuInflater inflater = getMenuInflater();
    inflater.inflate(R.menu.main_menu,menu);
    return true;
}

Right click on res and you will android resource directory ->give directory name ->give resource type as menu : a menu folder will be created inside res, now right click on menu->new-> menu resource file->file name-> ok . Now you see the menu xml file inside res/menu/yourfile.xml