Generally speaking, Sound design is a very crucial part of the film making indeed. It is an audio post-production process. For instance, it can improve your film narrative story or create a completely new one. As a result, we can add anything to a certain scene. For example, the breeze of the whispering wind, likewise, the noise of flying leaves or a bird song. In short, instead of listening to an accidentally recorded noisy tractors or airplanes passing by.
Similarly, for example, the claps of an audience might be also added to a film scene to obtain more impressiveness than the original clapping by the actors, that were recorded on the film set. On the other hand, is foley. Which is generally performed by the foley artist and recorded by an audio engineer. Opposite to a sound design process where normally are audio samples and sound synthesis used. We are seeing, what we are hearing!
Film Sound Berlin