In Settings, you can adjust what is shown on the external display and what happens when you flip the phone open or closed.
The easiest way to change how your screen looks is to touch & hold a blank space on the home screen of your external display.
You can also change the look in Settings.
Go to Settings > External display > Lock screen or Home screen.
If your wallpaper shows app icons on the home screen, you can change them.To change which apps show on the external display home screen, tap an existing app to remove it, or tap 



You can change the skin for your music player.

When your phone is unlocked, swipe the external display to move between panels of information. You can also tap shortcuts to jump directly to a panel.
Go to Settings > External display > Panels, then:


To quickly rearrange panels, unlock the external display, touch & hold its home screen, then tap Manage panels.




Adjust shortcuts:


When you flip the phone closed, your screen automatically locks, and when you unlock the external display, you are back on its home screen. If you want to keep the external display unlocked and continue using the app on it, then set the app to transition.

Select how you want the app to transition between screens when you flip the phone closed:


Flip your phone open to answer an incoming call, and close it to end a call.
To change how your phone handles calls:
Adjust settings:

Sleep display lets you peek at the time, check notifications, and control media that's playing, using very little power. You can customize how you interact with the sleeping display.
Select the gestures you want to turn on the sleep display:



If you want to skip Sleep display and instead go directly to the lock screen, you can turn Sleep display off.
Turn Use Sleep display on or off.
If you turn it off, you can't use Desk display.