Explain the difference between colloquial english and formal speech or writing

Colloquail English writing are informal or contain informal or everyday language like what's up and mostly contain contracted forms of words and street terms. Examples of such writings are friendly letters or letters written to agemates like friends.                                                                                                        Formal writings on the other hand are written differently. All words are written in full form and the proper form of English is used. Example of such writtings are formal letters or letters written to people of high offices or authority.