Intonation is a word used to refer to how a sentence sounds. How a sentence sounds if it's a question sounds different from how a sentence sounds if it's a statement. If you say a sentence out loud, first as a question and then as a statement, you'll hear the difference in sound. That is intonation. You can find more information here: http://www.sil.org/mexico/museo/5ai-Intonation.htm
