since you followed the tutorial, I presume you have a screen that says Hello World.
that means you have some code in your layout xml that looks like this
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/hello_world" />
you want to display an image, so instead of TextView you want to have ImageView. and instead of a text attribute you want an src attribute, that links to your drawable resource
<ImageView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:src="@drawable/cool_pic"
/>