Informal writing is usually used in our everyday life to give messages to our friends or to our family, for example. Here are some examples of informal writing. Write a line or two of each. Write a note saying that someone called for your cousin and left a phone number to call back. Write a grocery list of items that you need in order to make a healthy snack when your friends come over for an afternoon visit.
More formal writing is used to invite special guests or to thank someone in writing.
Be sure that the letter shows your appreciation. Revise and edit your letter and write a final copy, ready to send. Address the envelope. If you are not going to send the letter, practice writing an address and your return address. Clever as a computer is, it's not nearly as complex as a human brain.