If you hail from the Windows world, one of the first questions you'll feel the need to ask about BSD is "what's the equivalent to Windows Update?" In the FreeBSD world, the corresponding procedure is a little more complex but a LOT more powerful and comprehensive. Thanks to the ports tree, your applications as well as your base system can all be updated in the same way, and completely under your control.
The first thing you need to do is update the ports tree using cvsup. This is a CRUCIAL first step to any update process, because you want to make sure you've got the latest sources before you start compiling them to replace your existing ones!
Once you've done that, you can use the portupgrade port to first check for newer versions of installed ports and then perform the actual upgrades.
(also see updating the system)
why portupgrade -a is BAD, BAD, BAD - (why is it?)