>I'm getting a domain name. What is the difference between these two?

The big three:
COM - commerical, but is commonly misused (example www.evandelay.com)
NET - network (including groups) or ISP
ORG - non-profit organization

I think it is best to use COM since user know it and expect it. Except if you are genuinely non profict or government. In the USA you guys also use GOV, MIL and EDU... which as not as common elsewhere. Or non-profits also use country codes.