What does a basic PC firewall do

A good explanation of What PC Firewall Can Do can be Found on official website of PC Firewall Software named 'ZoneAlarm' mean 'ZoneAlarm by CheckPoint.

As Per Their Front Page:

In a building, a firewall is a fireproof wall that acts as a barrier between one part of a building and another. The firewall's goal: to prevent a fire from spreading.

Similarly, a basic PC firewall acts as a barrier between your PC and the Internet. The PC firewall's goal: to prevent Internet threats from spreading to your computer.

Working in the background, a basic PC firewall monitors the traffic flowing through your computer's open door to the Internet. When anything seems suspicious, such as a request by an unknown source to connect to your PC, a basic PC firewall automatically identifies and blocks it.

A basic PC firewall not only prevents unauthorized access to your PC or network, it also hides your Internet-connected PC from view. And that helps prevent attempted intrusions in the first place.

Related Post is:

Why You Need A PC Firewall