How do firewalls function in protecting systems from unauthorized access?

Firewalls operate by monitoring incoming and outgoing network traffic and applying a set of predefined rules to determine whether to allow or block the traffic. They create a barrier between a trusted internal network and untrusted external networks, filtering out potentially malicious or unauthorized data packets. Firewalls can be set up to inspect packet contents, source and destination addresses, port numbers, and other parameters to enforce security policies. They help prevent unauthorized access, secure sensitive data, and protect against various cyber threats like malware, hacking attempts, and unauthorized access.