Tones (声调 shēngdiào)

And that’s why Chinese is considered as a tonal language. The tones (声调 shēngdiào) are very important in a syllable. One syllable can be pronounced in different ways depending on the tones that convey differences in meanings. In common speech there are four basic tones.

I will use the syllable "ma" as an example to show you how it's pronounced;

1st tone - mā
2nd tone - má
3rd tone - mǎ
4th tone - mà

The graphic mark of the four tones is always put on vowels; if the syllable contains only a single vowel then the tone should be placed directly above the vowel letter, as we can see in “bù” and “hěn”. If the tone is dropped over the vowel “i” the dot should be replaced by the tone mark, for example, “nǐ”, “nín” and “bīng”.

When the final of the syllable is composed of two or more  vowel, The tone mark should be then placed above the one vowel pronounced with a widest mouth opening, example “hǎo”, “měi”.

Some syllables are pronounced slightly and briefly, without any tone. This phenomenon is called “neutral tone”. It is located by the absence of a tone mark on the syllable. Example: “ma”, “ne”...

When there is one syllable with the third tone followed immediately by another syllable with a third tone as well, the first syllable should be pronounced in the second tone while the tone mark remains unchangeable.

For example:

nǐ hǎo            ---->    ní hǎo

hěn hǎo        ---->    hén hǎo

yě hěn hǎo   ---->    yé hén hǎo