An AudioSource is attached to the GameObject to play sounds in a 3D environment. To play the sounds we need an AudioListener.
The Audio Listener acts as a microphone-like device. It receives input from an Audio Source in the scene and plays sounds through the computer speakers.
Audio Listener can be applied to the game by:-
Go to Component->Audio->Audio Listener
In most of the applications it is attached to the Main Camera.
Sounds can be played in 3D or 2D and it is determined by the AudioImporter settings.