What is it?
Intonation refers to the pitch that is used to speak. English has a particularly wide pitch range that allows speakers to vary their pitch by making it rise or fall when expressing an utterance (e.g. sentence or question). Stress refers to an increased loudness for a syllable in a word or for a word in a phrase, sentence, or question.
Why is it important?
Intonation and stress are important because they assist in communicating additional meaning to an utterance. It helps to strengthen a specific meaning, attitude, or emotion in an utterance. A speaker can use intonation and stress to inform the audience that a particular part of what the speaker is saying is important or worth attending to.
How is it done?
Regarding intonation, a speaker can raise or drop the pitch in order to express different meanings. For example, the question “why is experiential learning taught like this?” can be said in two different ways to express two different meanings. The speaker can use a falling pitch at the end of the question on the word “this” to express a genuine question. Alternatively, the speaker can use a rising tone on the word “this” to express surprise or disagreement.
Regarding stress, a speaker can say a syllable of a word or a word in an utterance louder than other parts of the utterance to emphasize its importance to the audience.
See Examples