Anybody knows actual use of firewall?

Firewall protects the PC from unknown and unauthorized internet access by some applications. It also protects our pc by not allowing few site/apps to accessing out computer files.

firewall protects your PC from unauthorized sources to access your information. 

no

It is used to save the system from any kind of virus attack.

A system designed to prevent unauthorized access to or from a private network. Firewalls can be implemented in both hardware and software, or a combination of both. Firewalls are frequently used to prevent unauthorized Internet users from accessing private networks connected to the Internet, especially intranets. All messages entering or leaving the intranet pass through the firewall, which examines each message and blocks those that do not meet the specified security criteria.

http://www.webopedia.com/TERM/F/firewall.html

A firewall can help prevent hackers or malicious software (such as worms) from gaining access to your computer through a network or the Internet. A firewall can also help stop your computer from sending malicious software to other computers.

It is a security for saving system from Virus.

it prevents unauthorized access to your computer

to prevent intrusion from outer networks to your sub-net.Firewall apply required protocols or policies on network traffic that passes through your firewall to stop hacking and unnecessary conjestion of traffic

It is a software that checks information coming from the Internet or from a network, and then either blocks it or allows it to pass through to your computer, depending on the settings you have in your firewall software. It can help prevent hackers or malicious software (such as worms) from gaining access to your computer through a network or the Internet.

many antivirus is availalabe free and paid. What is special in firewall?

fire wall use karo to microsoft ko pata chal jata he we are using duplicte copy of win

checks information coming from the Internet or from a network

Firewall is protection shield of your computer. It will save your computer from harmful virues.

Firewall disallows entry of new programes and thus saves the system from any undesirable intrusions by virus. If you permit, firewall will let a particular priogram to enter.