Is firewall necessary in Ubuntu

[kittysacattack]

Do i need to install a firewall in Ubuntu, or is the system safe as is from a fresh install. I installed firestarter but dont know how to use it. I have 3 options eth0, ath0 and wifi0, i tried all 3 and ended up just using ath0 becasue it was the only one not to give me an error message.

 

[brian]

firewall is not nessesory, but ubuntu comes with one, forget the exact name but it is built in