Chinese language, in the wide meaning of this word, is spoken by a billion and a half people every day. I write 'wide meaning' because the language has several varieties that differ greatly as far as grammar, pronunciation, or vocabulary.

The most important variety is called pu tong hua ("people's language"), which is used by about 900 million people. It is the official language of the Peoples' Republic of China, the variety from the north-eastern part of the country, from Beijing. Television and radio programs are broadcast in this language, it is also taught in schools throughout China. This 'promotion' of one variety of Chinese serves as a tool for unifying the whole population of the country, because even now people from different parts of China sometimes can have problems with communicating with each other.
For example, the word 'hello' (eg. at the beginning of a phone call), in putonghua is pronounced 'wei,' in guangdong hua (Cantonese variety of the Chinese language) it is 'wai.' But the word 'to go' is pronounced, respectively, 'qu' and 'hui.'
The differences between varieties of Chinese are compared to differences between French and Spanish, some words are the same or similar, some are completely different.
Other important varieties of Chinese are shanghai hua, the Shanghai variety, which is used by about 50 million people, guangdong hua, which is used by people in Guangdong province and Hong Kong, about 70 million. This variety is also the most frequently heard in Chinese communities abroad, as the majority of Chinese immigrants seem to be from the south.
Chinese is a tonal language, which means that the meaning of a given word depends on the intonation, with which the word is pronounced. Classic example, the word ma can mean 'mother,' horse,' or 'question-forming particle.'
Because of that foreigners often have problem with communication. In most instances the locals take into account that Chinese, apart from tones, also has sounds that don't exist in other languages, and they are willing to guess what we are trying to say, but sometimes they refuse to understand even 'good morning,' because the tones are wrong.
The factor unifying the different varieties of Chinese is writing. Regardless of pronunciation every word has a symbol, that looks the same everywhere in China (in the Mainland, about that in a moment).
Traditional, old Chinese, has over fifty thousand characters, thankfully the vast majority is now obsolete. In 1950s the government of China introduced a reform of writing, whose aim was the reduction in the number of illiterate people. The reform included a few thousands most commonly used characters, which have been simplified so it was easier to write and remember them. (I will not mention the details of writing here, there are course books and websites that teach that).
At the same time a system of writing Chinese using Latin alphabet has been introduced. Pin yin, that is the name of the system, was intended to make learning easier, for children and for foreigners. It is not an ideal solution, because pinyin does not show the variety of characters. For instance, Chinese has over a hundred and twenty characters pronounced yi, or over eighty words ji, every one of them is written in a different way, and of course every one had a different meaning. In pinyin, without context it's impossible to understand which symbol (which word) has been written.
Pin yin is also used for typing on a computer. Words are written in the Latin alphabet, eg. 'ma,' then from a list (a window with all the 'ma' characters opens) you choose the one you want to use.
In Hong Kong, on Taiwan, and in the majority of Chinese communities abroad this reform has not been accepted and the old, more complicated version is still used.
To cheer you up I shall add that only about a thousand characters is enough to read a newspaper. An average Chinese person knows about 4-5 thousand, an educated person - about eight thousand.
10.2005