Chinese includes many regional language varieties, the main ones being Mandarin, Wu, Yue, and Min. These are not mutually intelligible, and many of the regional varieties are themselves a number of non-mutually-intelligible subvarieties. Jerry Norman estimated that there are hundreds of mutually unintelligible varieties of Chinese. As a result, many linguists refer to these varieties as separate languages.
‘Chinese’ can refer to the written or the spoken languages. Although there are many spoken Chinese languages, they use the same writing system.  Differences in speaking are reflected in differences in writing. Official China adopts a similar policy to the one in the Soviet Union. All official documents are written in Mandarin, and Mandarin is taught all over China. They have one standard language for all of the schools in China and Taiwan. It is also a standard for language teaching in some other countries. In English we call it Mandarin. In China they call it “Pǔtōnghuà” or “common to everybody speech.” In Taiwan they call it “Guóyǔ” or “language of the whole country”. They need a standard language because otherwise many people would not understand each other, despite being in the same country .
Chinese is used by the Han people in China and other ethnic groups who have come into China and are declared Chinese by the Chinese government. Chinese is almost always written in Chinese characters. They are symbols that have meaning, called logograms. They also give some indication of pronunciation, but the same character can get very different pronunciations among the different kinds of Chinese. Since Chinese characters have been around for at least 3500 years, people in places far from each other say them differently, just as “1, 2, 3” can be read differently in different languages.
Chinese people needed to write down pronunciations in dictionaries. Chinese does not have an alphabet, so how to write down sounds was a big problem in the beginning. Nowadays the Mandarin language uses Hanyu pinyin to represent the sounds in Roman letters.