Slangs are nothing but Informal words or expressions that are used in the spoken rather than in the written English. As they are strictly informal, you might want to use them mostly with friends, colleagues or people close to you. You'll want to refrain from using slangs with your boss, teachers or elders. It is important to also know that slangs are not unique words. They are, however, derived from other common English words or maybe other slangs too.
Word of Mouth: Workplace Idioms for the Non-Native Speaker
A number of years ago when I began to work at several corporations teaching ‘accent reduction’ to non-native speakers of American English, I was often asked to define informal, everyday expressions. These employees were eager to know the meaning of idioms and slang that they had heard their colleagues use in the workplace.
With more than 7,000 definitions, this book provides a definitive guide to the use of slang today. It deals with drugs, sport and contemporary society, as well as favourite slang topics such as sex and bodily functions. In this fully updated fourth edition of the highly acclaimed Dictionary of Contemporary Slang, language and culture expert Tony Thorne explores the ever-changing underworld of the English language, bringing back intriguing examples of eccentricity and irreverence from the linguistic front-line. "Thorne is a kind of slang detective, going down the streets where other lexicographers fear to tread." Daily Telegraph