How audits actually work — the AUD section of the CPA exam. The audit opinion and when each type is issued (unmodified, qualified, adverse, disclaimer), audit risk and its components (inherent, control, detection — and how the model drives testing), materiality, internal control and the COSO framework, tests of controls versus substantive procedures, audit evidence and its hierarchy, sampling, management assertions and the procedures that test each, independence and professional ethics, going concern, and the difference between audits, reviews, and compilations. Every explanation names the concept, diagnoses the tempting confusion (control risk vs detection risk, existence vs completeness), and leaves a portable rule. Original questions from the public AICPA blueprints — never real exam items. Independent practice; no pass guarantee. Educational only.