Formal English and Informal English differ in the tone, and the usage of English. When do you use Formal English and when do you use Informal English?
Usually when we talk about the two kinds of English it is in the context of writing. Formal English is used when writing a report, e-mail or a business communication. When you are writing for business, you need to use proper spelling, grammar, sentence structure and punctuation. Your writing must be free of jargon, and be to the point. An example of a letter in Formal English would be a complaint letter to a company. For example, if you bought a fresh loaf of bread, and while eating it, you found mold. You would use Formal English to write a complaint to the bread manufacturing company.
Informal English is used when you are on social networks such as Facebook, Google+ and Twitter. You can also use it when you are writing e-mails to friends and family. When you use Informal English, you can use jargon, abbreviations, creative sentence structure and improper spelling. An example could be writing an e-mail to invite your friends to a BBQ. “I’m having a BBQ this coming Sunday. Wanna come?”
You might want to be careful about being too free with informal English on Facebook however, Prospective employers can look up your profile, and based upon what they see, decide whether to ask you to come for an interview or not. The rule in writing is usually, when you are in doubt, use Formal English rather than Informal English.