Explain the concept of intonation in linguistics.

Intonation is the "music" of speech. It is one aspect of pronunciation, and it is the oral equivalent of punctuation.
Teaching intonation is a fairly complex undertaking. There are few clear rules. Two that I usually teach in my classes involve the intonation of questions. Wh-questions have a falling intonation, and Yes/No questions have a rising intonation. Intonation is not just in questions, however. It is present in other utterances as well, such as giving orders (falling).
The best approach for the teacher is to model—not explain—intonation. Students need to hear examples. Intonation often conveys feeling, so loud and angry examples are often best: "You are an hour late!" When intonation gives us information about the speaker's attitude, this is known as attitudinal function.
Many language learners use flat intonation, so most courses should include intonation work. One way for students to work on this is by drawing arrows to mark intonation on dialogues. And the whole class enjoys the practice when intonation is exaggerated in funny ways. Teachers want students to sound polite, friendly, and interested, so intonation is an important part of language learning.
Intonation is best taught as part of work on other materials. An entire lesson on intonation would likely be dull and otiose. Teaching intonation can be frustrating because student progress in this area is usually slow.