NEVER put your real name. ALWAYS use a nickname/pseudo. For a very simple reason :
I don't know how old toi are but know that if toi put your real name, it shall remain on the net. And once you're old enough to seek a job, recruiters Google your name. If they stumble on your FF.net stuff, they may think toi are strange/weird/unsuitable for the job. I mean, toi may write whatever toi want, the way toi want, but be careful as some people may not understand that hobby of yours.
That's what I do as I do not want any employer to find out what I write (mature, steamy, adult, violent stuff) - they would think I'm mental.
So be careful. Very careful. That's the conseil I give to all youngsters that venture on the net. toi shall leave traces on the net so hide them well.
As for your question about making account with fanfiction.net Once after toi put your information,you can makeup any pen name toi want to,it don't have to be your name unless that's what toi want.I been with them since 2005 and I just made up my own pen name.I weither make up a pen name instead of using my name because it makes it plus fun! My pen name is PocahontasJohnSmithForever,yeah it's long but that's what I like.I was thinking of changing my pen name here recentaly but since I made some Friends there and they already know me par that pen name, I decied not to.I just didn't want to get anybody confused par changing my pen name and saying in messages of what my old pen name was. I might change my mind later but for now it's gonna stay the same.And yes toi can change toi pen name any time toi want to as it well under your settings once toi sign up. toi can even add a Avatar which is just little picture par your pen name. Anyways I hope this helps!
It can be anything toi want it to be, like what you're a fan of, maybe add a little fanfiction to it, unless someone has already taken it, but be careful. toi can even change it if toi don't like it once you're done. Simple as that.