Examples of friendly letters can be found at LetterWritingGuide.com and StudyZone.org. Both sites also include instructions for writing friendly letters, and StudyZone.org includes labels on the required sections of the letter.
A writer uses an informal tone in a friendly letter, and the recipient is typically someone the writer knows well. The letter usually contains a heading with a return address and the date when the writer sent the letter. This is followed by a salutation, in which the writer addresses the recipient of the letter. Next is the body of the letter, which contains the bulk of the message. Following the body is the closing statement and the writer's signature.