I am sorry that I am such a newbie, but can somebody explain what a GMO is?
GMOs are like a new "skin". A simple appearance change, nothing else. You start out with your normal GMO + one extra, and you can get a new one by finishing missions for the netpolice (which you can apply for at the netpolice BBS).
usualy you should be at level 3 and then if you can finish one, you need to be at 3+3 per mission you complete. ie. 3, 6, 9, 12, 15 etc. so ya, new GMO every finished mission, new mission every 3 levels.
With a GMO, you can make your navi look like anything you want, so long as it isn't a ripoff. Back in the day, I had a Ninja GMO that gave my old navi ninja clothes, and Tom had one that completely transformed his navi into a Metool. That should give you some idea of what kind of range these things have.

Like they said, you get one blank GMO file to begin with, and can apply for a new one on the Netpolice BBS every three levels. They'll have you complete a mission for them, and at the end you'll be awarded your GMO file.

You can only register as many different GMOs as you have blank GMO files. If you're at level 1, for instance, and just registered a GMO (let's say Ninja.GMO, just for the heck of it,) you can't register another one until you reach level 3 and complete a mission for the Netpolice, getting a blank GMO file as your reward.
King is absolutely correct. And since you're a newbie, I would like to tell you about questions. We have a "Everything you ever wanted to know" thread, which is a thread pinned and dedicated to any and all questions you may have. I'm not saying, "Do this or die", but I'm saying that people pay a lot more attention to a bigger thread.

But then again, there's always King to help out. :lol:
GMOs are good when you want to look like something. Think of them like Alternate outfits for certain games.
or.....costume play! ie. baseing your GMO off of something you like to watch, some kind of creature you like, etc. me? it's cats or anything furry. *looks around and is shot* owie.....
Thanks, everyone!