This document provides information on how to vary sentence structure to make writing more interesting. It discusses using simple, compound, complex, and compound-complex sentences. Simple sentences contain one independent clause, while compound sentences contain two independent clauses joined with a conjunction. Complex sentences have one independent clause and one dependent clause. Compound-complex sentences contain two or more independent clauses and one or more dependent clauses. The document provides examples of each sentence type and guidelines for using commas with different clauses.