First off, go to the FreeBSD ports page and read up on the ports system. Lots of good info there.
Then, you need to download the ports. I think using portsnap is the way to go these days. So, as root, you run:
# portsnap fetch
# portsnap extract
You can read about using portsnap here:
http://www.freebsd.org/doc/en_US.ISO885 ... tsnap.html
There's also several entries in the PCBSD FAQ about using ports and their pre-compiled brethren, packages.