To prepare to run and test your Flutter app on the Android emulator, follow the following steps.
Go to Tools > AVD Manager (Android Virtual Device (AVD) is a configuration that defines the characteristics of an Android device that you want to simulate in the Android Emulator)
Or you can click on the icon as shown on the image below to open AVD Manager.
Click on Create Virtual Device…
Select a device type and its configurations and click Next.
After that, select the System image.
Next, add a name to your device.
Finish the creating of your virtual device.