ISO/IEC 27001 is the international standard for an information security management system (ISMS): a documented, audited process for identifying information security risks and controlling them, not a single product or checklist. A business seeking certification defines the scope of what the ISMS covers, runs a formal risk assessment, applies controls proportionate to those risks (drawn from the standard's Annex A control set), and has the result independently audited by an accredited certification body.
Certification is not permanent. It runs on a three-year cycle: an initial two-stage audit, then annual surveillance audits to confirm the ISMS is still operating, and a full recertification audit at the end of the cycle.