This document discusses the structure of sentences and parts of a friendly letter. It defines four types of sentences: simple, complex, compound, and simple. A simple sentence contains one independent clause, a complex sentence has one independent clause and at least one dependent clause, and a compound sentence contains at least two independent clauses. The document then explains the five parts of a friendly letter: heading, greeting, body, closing, and signature. It provides an example of writing a reading response letter about a memoir book or movie.