The Sound Block allows you to play a particular note, tone or even an audio file. You will be able to play the sounds for different length of time(S) as well as different volume(V). You can set it on loop or to play once using the flag image above (F). Music can be formed by placing the notes one after the other.
You could also use it for functional purpose in order to find the increase or decrease of values. For example, the light sensor will detect black and the sound produced will be at a higher frequency. This will help to identify the difference in light value when running the EV3.