The previous versions of Windows like Windows 2000 and Windows 98 did not have a built in firewall. A firewall basically is a program which monitors your computer and internet connection and helps you block any illegal contact to your computer.
A firewall manages the data that comes to your computer from many ports that your computer uses to exchange information from the outside world. The firewall makes sure that only the necessary ports are available to the outside world, and blocking the other ports so that they cannot attacked by malware. Though you can select and unblock the necessary ports which are required by specific programs.
You should not forget that releasing to many ports will expose your computer to malware as well as reduce the security of your computer.
A firewall manages the data that comes to your computer from many ports that your computer uses to exchange information from the outside world. The firewall makes sure that only the necessary ports are available to the outside world, and blocking the other ports so that they cannot attacked by malware. Though you can select and unblock the necessary ports which are required by specific programs.
You should not forget that releasing to many ports will expose your computer to malware as well as reduce the security of your computer.