Basic questions on Ubuntu

[Faun]

First step is to check what all ports are open/filtered
install nmap and do a simple

nmap <your_ip_address>

Now you will get a better picture of what to filter and what not to filter.

Btw if you really want to try the easiest approach then install firestarter (its a great GUI firewall, you will be in no time setting up your rules easily).

 

[gary4gar]

@Sridhar_Rao
why you worry so much?
i am using Linux almost 15hrs a day from past 2years with any firewall & antivirus.
i have also disabled phishing filter as it reduces speed of firefox.
still, i am pretty much safe

also, if you are fearing unknown command you could use a Search engine like google.com or man pages.
for example:
if someone on a IRC, says to to run this code saying that it would clean up temp files.

sudo rm -rf /

you can google it, check man rm

here is Youtube video
www.youtube.com/watch?v=wWOjmvWPRvQ


the thing is keep your eyes open