If what you want is to duplicate your screen: To duplicate the screen we will go to the right area of the window and configuration and browsing through it, we will have to identify the section “Multiple screens”.
There we must choose the option "Duplicate these screens"
In this simple way, we will have duplicate screens on our device.
We must bear in mind that if the screens are of different sizes, the resolution may be negatively affected by the image on the larger screen due to the smaller one.
On the other hand, if you want to extend these screens, you have to: you must go to the "Multiple screens" section and display the options. Here we will have to choose "Extend these screens"
This will show a new desktop on each of the two screens.
If we try to drag a window with the mouse, we will verify that we can move it from one screen to another, even being able to expand it until it takes both screens. Ideally, to extend a screen is to have two of the same resolution and size, so you will see an enlarged and perfectly fitted image.