Every syllable in Standard Chinese has one of four distinctive "tones" or patterns of pitch, The only exception to this rule is that a syllable loses its inherent tone when it is unstressed. The tone is just as much a part of a syllable as the consonants and vowels and performs the same function--signaling the meaning of the syllable. In other words, difference in tone between two syllables can signal a difference in meaning, just as a difference in consonants or vowels does.
It will be difficult at first to appreciate fully that a tone is something that belongs to a syllable rather than something that merely happens to it. This is because the only use of pitch patterns in English is for intonation of entire sentences, affecting only the meanings of whole sentences, for example, the rising pitch at the end of "Spinach is delicious?" has nothing to do with the meaning of the word "delicious" but tells us that the whole sentence should be interpreted as "Are you saying that spinach is delicious?" It may be difficult at first to remember the tone of a syllable as well as you remember the consonants and vowels. This is because you have to develop the completely new habit of marking tones In your mental dictionary.