The document discusses the four types of sentences: simple, compound, complex, and compound-complex. It defines each type based on whether they contain independent clauses, subordinate clauses, or both. Simple sentences contain one independent clause, compound sentences contain two or more independent clauses, complex sentences contain one independent clause and one or more subordinate clauses, and compound-complex sentences contain two or more independent clauses and one or more subordinate clauses. Examples of each type are provided for illustration.