"China" is a noun that refers to the country of China. If it has a lower-case 'c', it's a synonym with "porcelain". "Chinese" is the adjective form of "China", but it can also be a noun refering to the language of China (中文). "Chinese" can technically refer to any Chinese language (Cantonese, Min Nan, Hokkien etc.), but nowadays most people will understand it to specifically refer to Standard Mandarin (Putonghua), although in the past it was used more often to refer to Cantonese (because Guangdong had the most contact with the West). You CANNOT use "Chinese" as a noun meaning "Chinese person) (中国人) ie. you can't say "I am a Chinese"; you have to say wither "I am Chinese" or "I am a Chinese person". "Chinese" always begins with a capital letter.