Mandarin is a tonal language with four distinct tones:
1 - high level - mā
2 - rising - má
3 - rising and falling - mă
4 - falling - mà
There is also a 5th tone which is neutral.
The tone determines the meaning of the word or syllable. For example:
睡覺 shuì jiào
means "sleep," but
水餃 shuǐ jiǎo
means "dumplings."
Variations
When two 3rd tones are used together the first 3rd tone becomes a 2nd tone:
你好 nǐ hǎo (hello)
becomes
ní hǎo.
Yi 一 (one) is a first tone syllable, but when it comes before the first, second, or third tones it is pronounced in the fourth tone:
一些 yì xiē (a few)
一直 yì zhí (continue; straight ahead)
一點 yì diǎn (a little)
When yi 一 comes before a fourth tone, it is pronounced in the second tone:
一定 yí dìng (certain)
Bu 不 (negating adverb) is a fourth tone syllable, but when it is used before another fourth tone, it is pronounced in the second tone:
不好 bù hǎo (not good)
不謝 bú xiè (don’t mention it)