The document discusses the grammar rules for using "would rather" and "had better" to rewrite sentences. It provides examples of rewriting sentences from "should", "ought to", and "prefer" using "would rather" or "had better" instead. It also prompts the reader to complete two sentences using those phrases appropriately. The key idea is that "would rather" and "had better" can be used as alternatives to other expressions involving preferences, obligations, or suggestions.