Creating a db on my newly installed postresql on OS X

Hi

Im totally new to postgresql. I installed 8.4.3 via MacPorts, and it told me to run this command to have postgresql start at boot:

sudo launchctl load -w /Library/LaunchDaemons/org.macports.postgresql84-server.plist

I can see with a ps command that there are something runing. So what next? I can read that I must use initdb to create a database, and give it a path to a file/directory where the data will be stored, but will the running postgresql server then know where this database/data is?

What are the next steps to get me up and running?

Med venlig hilsen/Best regards
Søren Neigaard 

If I'd known computer science was going to be like this, I'd never have given up being a rock 'n' roll star.