The best place to do your research is
http://www.copyright.gov. It is the official government site and can answer just about any question you can ask, or at least point you in the right direction to find the answer. And comics fall under the visual arts category.
Also use your local libraries if you really want to delve into the subject. Any decent library should have a few books on copyright (mine has four) and a bunch of technical law books that cover the subject in legalese.
Technically you don't even need to file a copyright with the government. Any work of creativity is automatically copyrighted the moment it is created. Getting an officially registered copyright does help you if you find yourself in a legal battle over ownership, but to be honest that is highly unlikely.
Now the following isn't proper legal acvise, but what I've picked up doing mini-comics and talking to self publishers. There is a cheap easy form of copyright. Take a photocopied version of your work. Put it in a quality envelope (one of those thick yellow business kind). Seal it shut. Go to your local post office and send ti to yourself through registered mail. Now the government has a record of when the work was finished and from where it was sent. Keep the envelope sealed!! Should there ever be a question as to when and who created the work you have the sealed dated envelope to open when you go to court (which, once again, is highly unlikely).
I've tried to give answers to any question I could think of. If you have anything more specific, just ask. Or look it up. Or ask an intellectual property rights lawyer. You know whatever.
