firewall question

[Gerhard Magnus]

I'm running Ubuntu 12.04 after switching from Fedora and am confused by 
the way Ubuntu handles its firewall. For example, ssh worked fine 
without my having to open port 22, which I had to do explicitly with 
Fedora in terms of allowing ssh as a trusted service.

For Ubuntu, how can I determine which services are trusted by default? 
Is a service immediately trusted when it's installed and its ports open 
whenever it's started -- all in a way that's "transparent to the user"?

Also, could some one direct me to a link that explains the basics of 
Ubuntu's firewall policies?