Thank you letter is type of letter written to express our gratitude to someone for a good deed they have done. In the exam you may be asked to write a thank you letter for various situations. But their task may not say write thank you letter. Instead, there may be task in the form of write a letter to tell that you were happy with. You write this type of letter in a positive tone you praise certain things and talk about their positive impact on your life. Depending on who you are writing to you can write a letter in a formal style. Below you can see the difference of some words in the type of letters.