The method of setting up a computer extension screen mainly depends on your computer operating system and hardware configuration. Here are several common methods for setting up：
Method 1 (applicable to Windows system):
1. Connect an external monitor: Use VGA, DVI, or HDMI cables to connect the external monitor to the computer’s graphics card interface.
2. Enter Display Settings: Right click on a blank space on the computer system desktop, select “Display Settings” or click the “Start” button in the lower left corner, select the “Settings” function item in the left menu bar, enter the Windows Settings interface, and click the “System” tab.
3. Identify monitor: After successful connection, two monitors can be seen in the display settings interface.
4. Expand displays: Select “Expand these displays” under “Multi monitor settings” so that both displays can display normally.
Method 2 (Set up through Control Panel, applicable to Windows system):
1. Open the control panel: Open the control panel on the computer.
2. Enter System and Security: Open “System and Security” in the control panel interface.
3. Enter the system: Find “System” in the system and security interface and click to enter.
4. Set up multiple monitors: Click on “Display” on the left and select “Multiple Monitor Settings” on the right. Click on ‘Expand these displays’ and then select’ Keep changes’.
Method 3 (Expanding Screen via Wireless Connection, Suitable for Windows Systems Supporting Miracast):
1. Enter Display Settings: Similarly, on the computer system desktop, right-click on a blank space on the desktop and select “Display Settings”.
2. Select wireless display: In the display settings interface, find the “Multiple Display Settings” column, and then click “Connect to Wireless Display” below to search.
3. Connect wireless display: Select the device you want to connect to from the searched wireless display devices, and click on it to connect.
Please note that the specific setup steps may vary depending on the operating system version or hardware configuration. If you encounter any problems during the operation, it is recommended to consult the manual of your computer or monitor, or search for specific tutorials online.
In addition, if your computer or monitor does not support certain specific connection methods, you can buy some additional hardware (such as converters or adapters) to achieve the function of expanding the screen.