There are lots of different singing styles in the world. Each one has a different technique. In Western classical music singers learn to sing in a bel canto voice which uses lots of resonance in the head and makes a smooth sound. Bel canto was used in Italian opera. Later, in the 19th century, Richard Wagner wrote operas in which the singers needed to be more dramatic. Opera singers today can have different kinds of voices: bel canto, lyrical, dramatic, coloratura (extremely high and light) etc.