The document discusses different types of sentences: simple sentences contain a subject and predicate and express a complete thought. Compound sentences contain two independent clauses joined by a coordinator such as "for, and, nor, but, or, yet, so". Complex sentences have an independent clause joined by one or more dependent clauses, which do not express a complete thought on their own and usually begin with a subordinating conjunction or relative pronoun. Compound-complex sentences contain two independent clauses and one dependent clause.