The main usage of an Emulator is, as a platform to execute the Android application on a desktop system. That is where an android emulator gets into the picture. You would not be able to enjoy your game or check out the minute technicalities of the program. Suppose you want to play a game or run a program, the small size of the android device and its limited specifications tend to pose a big hindrance.
To put it in layman’s terms an Emulator is essentially an Android Virtual Device that is specifically designed to represent any Android device on a computer system.