Our communication with other members of a society depends from our facial expression (smiling; tearing; laughing…) sound of our voice (upset; angry; happy; sad; worried; afraid; tired…), gestures (shaking hands; kissing; hugging; warning; giving a directions; greeting someone; hitchhiking…) and our speech as well.
In casual life we divide language onto formal and informal. Talking about formal body language we can mention official gestures (policeman stretching his hands with his palms up = giving a permission to driver to continue his way; hitchhiker stretching a right hand with a thumb up = stopping a vehicle; teacher shaking with his forefinger = giving a warning…) which are known by most of people because these gestures are from common life and they have very significant meaning. In a past, people from high society were thought not to show their fears and feelings in a public, they were thought a formal behavior. Nowadays we can still see politicians, Royalty, officers and other important people who keen on strict rules of a behavior and a proper use of language. In formal conversations we use full forms of polite and appropriate words, and correct expressions.
Informal language, either body language or speech, is more common among especially young people. They feel more comfortable and open-minded while using this style of communication. Schools (teachers; students; staff), work places, and mainly households are good examples where informal language is used. The communication is usually between two or more human beings of a same or similar social statuses. They use slang words, shortened sentences and words, and informal gestures (like hugging; kissing; punching as a part of greeting, high-fives and so on…) in a public.
To sum up, the style of language depends from the social status of a human and an environment where one lives, works and spends a time.