How to connect Samsung DeX with Galaxy S10 Series?

You can use a wireless keyboard/mouse to flow from the external display to the Mobile Device’s screen

Launch the Settings App > Samsung DeX > Mouse/trackpad, and then select the Flow pointer to phone screen switch to activate it.

You can also use the external keyboard on the Mobile Device’s screen.

Using S10 Series as a touchpad

You can use your Mobile Device as a touchpad and operate it with your fingers. On your Mobile Device, drag downwards from the top of the screen to open the notification panel and tap Use your phone as a touchpad.

ㆍYou can use the touchpad only when using Samsung DeX mode
 

ㆍIf your Mobile Device’s case has a front cover, open the front cover to use your Mobile Device as a touchpad. If the front cover is closed, the touchpad may not work properly

ㆍIf your Mobile Device’s screen turns off, press the Power key to turn on the screen

a) Orienting the touchpad

When you are using your Mobile Device as a touchpad, you can use it in either the horizontal or vertical alignment.  To rotate the touchpad, rotate the smartphone or double-tap  Rotation icon.

b) Using Mobile Device while using the touchpad 

You can use Apps on your Mobile Device even while it is being used as a touchpad. On your Mobile Device, drag upwards from the bottom of the screen to show the navigation bar. Then, tap the Home button to move to the Home screen, and select the Apps you want to use.

c) Using Mobile Device to perform texting tasks

When you enter text to send messages, create notes, or perform other tasks, a screen keyboard will appear automatically on
your Mobile Device’s screen without connecting an external keyboard. If the keyboard does not appear, select the Keyboard icon on the
quick access toolbar.
 

Monitor screen is cropped or color satuation is different when connecting with Galaxy S10 Series via Samsung Dex Station

If your TV or monitor screen is cropped or displaying different colors, go to Settings menu of the relevant display, and try to
resolve the issue to some degree via the Color/Resolution settings or Screen Size settings.