In the drawable folder, there are some icons, as shown in the following screenshot:
These are the usual icons, but also the ones that appear in the menu of the navigation drawer. We will not take the trouble to change these, but if you want to personalize the icons in your app, it should be plain by the end of this exploration how to do so.
Next, open the res/menu folder. Notice that there is an extra file titled activity_main_drawer.xml. This next code is an excerpt from this file, so we can discuss its contents:
<group android:checkableBehavior="single">
<item
android:id="@+id/nav_camera"
android:icon="@drawable/ic_menu_camera"
android:title="Import" />
<item
android:id="@+id/nav_gallery"
android:icon="@drawable/ic_menu_gallery"
android:title="Gallery" />
<item
android:id="@+id/nav_slideshow"
android:icon="@drawable/ic_menu_slideshow"
...