Hi, I was hoping someone could help me out on this one. I need to make a server very secure adn I need to close all ports I don't really need. Here is what my server will offer:

WEB PAGE SERVICES (Apache, perl, cgi's)
FTP conectivity
SSH "
DNS
MAIL SERVICE (Using Q-mail, MYSQL)

Now, I need to leave only this ports and services open on my machin, to have it "hacker proof". Anyone know where I can get an easy to understand way to do this? (TUTORIAL with commands etc) I'm new to linux and don't know that much. Thank you.