Firewalls protect networks from cyber threats by monitoring and controlling incoming and outgoing traffic. They act as a barrier between trusted internal networks and untrusted external sources, allowing only authorized data through. By employing various filtering techniques, firewalls can block malicious traffic, preventing unauthorized access and attacks such as malware and phishing. Additionally, they can log and analyze network activity, providing valuable insights for security assessments. Regular updates and configurations are crucial to ensuring effective protection against evolving cyber threats.