Here's a good page about the comma and why you might want to use it.
http://www.eskimo.com/~scs/cclass/int/sx4db.html
I can't help thinking that people who are new to the Arduino and have never done any programming of any sort might do better to play around with something like Processing first. Otherwise you're trying to learn programming at the same time as wondering if you've plugged the right wires in the right place.
Andrew