Firewalls act as a barrier between the public internet and your private computer or network and block threats including some viruses.

A firewall watches these ports to make sure that only safe communication is happening between your computer and other computers online. If it sees something dangerous happening it blocks that port on your computer to make sure your computer stays safe from the person who is trying to hack into your system.

An easier way to understand a firewall would be to picture your computer as an apartment complex. At the front door of this complex there is a security guard. Every person who enters the complex must pass this security guard. If the security guard recognizes the person entering as a resident he allows them to pass without saying anything. If, however, the person entering the complex is unknown to him then he will stop that person and ask for identification. If they have no business being at the apartment complex he escorts them from the building.

If you are not currently using firewall your computer will get hacked into - that's a guarantee.