Cantonese actually refers to Guangzhou dialect, also known as vernacular. Vernacular and Putonghua have different grammars and syllables. There are only four tones in Mandarin and nine tones in Cantonese. Mandarin has a tongue sound, while Cantonese has no rhyme. This is why you can understand everything in Cantonese and some words in Mandarin.
Guangdong, referred to as Guangdong for short, is the capital of Guangzhou, a provincial administrative region of People's Republic of China (PRC). Guangdong is named after the ancient place name "East of Guangxin". Located in the south of Nanling and on the coast of the South China Sea, it borders Hong Kong, Macao, Guangxi, Hunan, Jiangxi and Fujian, and faces Hainan across the sea.