Informal is language we use personally or to people we know. Formal is addressing people.
Informal language is used to apply for jobs. For example, using language for jobs and interviews. Also used for sending texts and video chat for something that is important.
Formal is used for friends you know and for family members. sending texts to friends and video calling with friends.
Formal and Informal are two different things because of the word in front of informal and formal having no in front of formal.