What are the functions of auditors?

Auditors are supposed to plan and perform the audit to obtain reasonable assurance that the financial statements presented by management are free of material misstatement that are caused by error or fraud. They only provide reasonable assurance not a guarantee that there is no misstatement or fraud. If they auditor is auditing a public company they also have the responsibility to evaluate internal controls. In other words the auditor plans and audit, gathers evidence, and then makes a report stating whether or not they believe the financial statements are presented fairly.