Fish, like humans, can breathe too. However, humans use lungs, while fish use their gills. Gills are located usually close to the eye. They have these flaps on either side of their bodies that open and close to allow water through their gills and extracting the oxygen. Most gills have a bony substance in order to support the gills.
These gills act as a filter to allow in what is needed but then keep out debris and other unwanted things. Some larger fish have several pairs of gills on either side of their face. These include different kinds of rays and some sharks. There are some fish that breathe the air and some fish that do not have gills at all. They simply use other forms of respiration to acquire oxygen.