Echolocation is used by dolphins to detect other animals, food, and dangers. A dolphin can build an image of its environment before seeing the object.
Secrets of Dolphin Sonar. This is an interesting explanation about the dolphin echolocation.
Dolphins breath through a hole in the top of the dolphin head which is called blowhole
Dolphins communicate through sounds and whistles.There are several kinds of whistles that are used by dolphins to communicate.