ISO certification has been largely considered as a quality management tool which provides a kind of identity to company's quality management system. It standardises how businesses and organisations involved in commerce and industry manage information and processes. It simply means that organisation has met certain requirements.
What is 9001 and what is not ISO 9001? ISO 9001:2008 is a quality management system, not a general management system. While ISO does actually provide general management systems that help document, organize and define how a business will run its overall operations (such as ISO 26000), these systems are rarely a requirement for certain types of commerce as ISO 9001:2008 often is.
ISO audit is the basic tool to check the quality process system to ensure that organisation is following the requirements as prescribed. Once you take an ISO certification, ISO audit needs to be done on an annual basis.