Your "username" can be your nick, or more likely, your choice of identd username. Alt-O > Connect > IdentD > User ID. **NOTE** If you have the box checked there to use your e-mail as the ID, you will have to either uncheck that box or else go into Alt-O > Connect and change the part of your e-mail that appears before the @.
Avoid things that may look like spambots... kljhkjh or ASKJFD or khfdg87 or things like that. Just try different things until you find one that you can connect with.