With the "Side Air" function, users can use the iPad as a display to extend or mirror the Mac desktop.
Use "Side Air" to extend or mirror the Mac desktop
Follow the steps below on Macs and iPads that meet the system requirements for "Side Air". Users can use the "Side Air" wirelessly, but if you want to continue to charge the iPad during use, use the USB charging cable that comes with the iPad to directly connect the iPad to the Mac.
Start a "flight" session
If the user is using macOS Big Sur, click the "Display" menu or menu bar in the "Control Center", and then choose your iPad from the menu.
If the user is using macOS Catalina, click the "AirPlay" icon in the menu bar 
, and then choose your iPad from the menu. (If you don't see the "AirPlay" icon, choose Apple menu> "System Preferences," click "Displays," and then select "Show mirroring options in the menu bar (when available).")
Or, move the window directly to the iPad (as described in the next section).
Or, use the menu in the "Side Air" preferences to connect.
Switch to screen mirroring
By default, the iPad will display an extension of the Mac desktop. The user can move a window into it and use it like any other display.
To mirror the Mac display so that the two screens display the same content, please return to the "Display" menu or the "AirPlay" menu. During the use of "Side Air", this menu will display a blue iPad icon 
. Please select the option for mirroring the display.
End the "Side Flight" session
If the user is using macOS Big Sur, please return to the "Display" menu or menu bar in the "Control Center", and then choose your iPad again to disconnect.
If the user is using macOS Catalina, return to the "AirPlay" menu and choose the option to disconnect.
Or use the "Disconnect" button in the sidebar on the iPad or in the "Side Air" preferences on the Mac 
.
Learn more about how to use an external display. For example, you can use the Display preferences to arrange the display so that the iPad extends the left, right, top, or bottom of the desktop.
Move the window into the iPad display
If you hover the mouse pointer over the full screen button 
of a window , you can choose to move the window in or out of the iPad display. This is faster than dragging the window, and the window size will be adjusted precisely to fit your display.
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