This document discusses different types of clauses that can be used in complex sentences: noun clauses, adjective clauses, and adverbial clauses. Noun clauses are used in place of a noun, while adjective clauses modify nouns. Adverbial clauses indicate time, place, manner, cause, and condition using words like when, after, before, until, because, as, since, and if. Examples are provided for each type of clause. In complex sentences, clauses help expand sentences by adding details like description, time, place, and cause-and-effect relationships.