This document discusses the use of commas after introductory phrases. It provides examples of sentences using introductory phrases like "after it rains" and "in a rainbow." These phrases must be set apart from the rest of the sentence by commas. Introductory words like "when" and "finally" also require commas. The document includes a quiz testing the use of commas after introductory phrases and words in sample sentences. It concludes that introductory phrases and words must be set apart by commas.