How are Chinese and Mandarin different?

Here's the short answer: Mandarin is a form of the Chinese language. Some call it a dialect. Chinese is an umbrella language term that encompasses multiple dialects/languages, including Mandarin, Cantonese, Hakka, and more. When you look at it closely, there are actually over 200 dialects of Chinese!

mandarin is part of chinese, it is the most popular and commonly spoken across the country

chinese including mandarin and dialect.

Mandarin is the standard dialect in mainland China. Each province, city and sometimes even villages has it's own dialect, for example Shanghai has 上海话，Wuhan has 武汉话，Chongqing has 重庆话. Mandarin is the main form of Chinese used for official communications.

Chinese has a lot of dialects in different places in China. The most important difference among dialects is pronunciation. Sometimes Chinese people cannot communicate with each other with different dialects. So, Mandarin is needed. Mandarin is a kind of standard Chinese. Its pronunciation is based on Beijing dialect. Mandarin is also called common speech in Chinese. Even in antient time, we have antient Mandarin. Teachers teach students with Mandarin in all Chinese school. So, almost every one can speak Mandarin, and at the same time, some people can speak one or two types of dialects.