Firewalls provide an additional layer for network security. Without them, computers and other digital devices connected to a local network have a higher susceptibility to outside attacks such as malicious software, viruses, spyware and more.
The firewall layer for networks helps to monitor outside internet traffic coming into a local network. One way to think of a firewall is to understand its function like a police checkpoint. Traffic coming in has to go through this checkpoint. At the checkpoint, traffic is either allowed through or halted. This filter for incoming internet traffic which keeps harmful items out is the main purpose of firewalls.
There are many available tools on the market to perform this function, both on the paid side and the free side. One great, free firewall software is pfSense. It is open-source, secure to use, and does its job well.
If you are looking to make your network more secure, look into getting a firewall setup!
Firewall Image Source: https://upload.wikimedia.org/wikipedia/commons/5/5b/Firewall.png