Firewalls are one of the core components of cyber security, usually protecting the perimeter of the network, their role is to shield the organisations data from the outside world creating a safe environment for users.
Over the years firewalls have advanced to include more sophisticated methods of protection, moving beyond port and protocol inspection/ blocking to include deep-packet inspection that adds in application level analysis and intrusion prevention. If you choose so, they can combine with other security solutions to provide a comprehensive gateway protection including protection from zero day attacks.