Windows 10 (UWP) include SystemNavigationManager in Windows.UI.Core namespace for Navigation purpose only.

Because SystemNavigationManager is part of Windows Universal Platform, So, it’s supported by all device family running on Windows 10 including Mobile and PC.

For Single Page

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If you just want to handle navigation for single page. Follow the following steps

Step 1. Use namespace Windows.UI.Core

using Windows.UI.Core;

Step 2. Register back request event for current view. Best place for this is main constructor of class after InitializeComponent().

public MainPage()
{
    this.InitializeComponent();
    //register back request event for current view
    SystemNavigationManager.GetForCurrentView().BackRequested += MainPage_BackRequested;
}

Step 3. Handle BackRequested event

private void Food_BackRequested(object sender, BackRequestedEventArgs e)
{
    if (Frame.CanGoBack)
    {
        Frame.GoBack();
        e.Handled = true;
    }
}

For Complete Application at one place for single rootFrame

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Best place for handling all backbutton for all Views is App.xaml.cs

Step 1. Use namespace Windows.UI.Core

using Windows.UI.Core;

Step 2. Register back request event for current view. Best place for this is OnLaunched just before Window.Current.Activate

protected override void OnLaunched(LaunchActivatedEventArgs e)
{
    ...
    SystemNavigationManager.GetForCurrentView().BackRequested += OnBackRequested;
    Window.Current.Activate();
}
    

Step 3. Handle BackRequested event

private void OnBackRequested(object sender, BackRequestedEventArgs e)
{
    Frame rootFrame = Window.Current.Content as Frame;
    if (rootFrame.CanGoBack)
    {
        rootFrame.GoBack();
        e.Handled = true;
    }
}

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References- Handle back button pressed in UWP

Hope this is helpful to someone!