Intonation is the variation of spoken pitch. It's used for a wide variety of functions. They include the attitudes and emotions of the speaker, the difference between statements and questions and emphasis given to different parts of the spoken message. In many languages the intonation of questions and statement is very different.
Contrastive stress can be expressed with intonation. In the sentences He didn't finish. I did. the emphasis on the pronouns he and I serves to create contrast between the two. It's also common to put extra stress on I to give greater emphasis.
Wh-questions in English have rising intonation on the wh-word and falling intonation at the end of the question. English yes-no questions, however, have rising intonation at the end of the question. The question Where are you from? ends with falling intonation and Do you agree? ends with rising intonation.
Dependent clauses often have lower pitch than independent clauses. For example, in the sentence Mr. Howe (the former hockey player) was born in Canada, the information in parentheses is often uttered with lower pitch. This serves to distinguish the two clauses.
Intonation also has a psychological function. It organizes information into units that are easy to perceive. For example, you can have it in red, blue or black has pauses between the colours and falling intonation on black. This helps to communicate the message clearly and makes it easier to remember.
Intonation serves a number of different functions. The variation of spoken pitch in English differentiates sentences and questions. Intonation also helps to distinguish dependent clauses from independent ones, organizes information into units which aid perception and gives emphasis to different parts of the message.