Android Emulator :
Emulator is the Android device which is provided by the Android Studio to run the app within the system. Emulator have the same ability ,features , functions as that of Amdroid mobile . It also takes care of Responsiveness ability of the app by providing different type of Android Device Emulator .
AVD (Android Virtual Device) is the tool available in Android Studio which is used to make the Android Devices . Or there are other ways in Android Studio from you can go to Virtual Device Configuration to make the device as shown in images taking from Android Studio.
By clicking on Create New Virtual Device , the next window is Virtual Device Configuration on which you can make your device with required Android API level , Size of Screen , Android Version etc. shown in the images.
Problem will be discussed in Comment section.