How to make Toolbar not overlap other content in Android?

Add this to the view below the toolbar

app:layout_behavior="@string/appbar_scrolling_view_behavior"

Replace your <include layout="@layout/content_main"/> with this:

   <include layout="@layout/content_main" 
      android:layout_width="match_parent" 
      android:layout_height="match_parent"
      app:layout_behavior="@string/appbar_scrolling_view_behavior"/>