In spoken English intonation refers to the rise and fall of your pitch over the length of a thought group or sentence.
Using the correct intonation is very important because the rise and fall of your pitch conveys meaning to your listeners.
Many linguists say that spoken English has four levels of phonetic pitch: 1-low, 2-middle, 3-high, and 4-extra high.
Normal conversations use middle and high pitch patterns.
Low pitch often signals the end of a sentence. When your pitch falls at the end of the sentience is indicates certainty or finality. It tells the listener you have completed your idea.
If I say this sentence: “You need to GO now” with falling intonation it means I want you to go.
Extra high pitch is used to express contrast, emphasis or emotion. When your pitch rises at the end of a sentence it indicates uncertainty.
If I say this sentence: “You need to GO now?” with rising intonation it means that I’m uncertain or surprised that you want to go.
Here are some more examples of English intonation patterns.
One of the best books for learning and practicing the intonation of spoken American English is Ann Cook’s American Accent Training