The document defines parallel structure as using the same pattern of words to show that two or more ideas have equal importance. It provides three rules for using parallel structure: 1) elements in a parallel list must be joined with conjunctions and use the same grammatical structure, 2) elements that begin with clauses must continue using clauses, and 3) lists of actions should use the same verb tense. Examples are given to illustrate correct and incorrect uses of parallel structure. The document concludes by stating that parallel structure adds clarity and readability to writing.