Copyright is a legal protection available to anyone who creates an intellectual property. This can be anything from a painting, drawing, song, poem, book, or comic books stories and characters. Copyright is in place as soon as the work is created; there is no need to register to enjoy this protection. Registering your comic book characters and stories, however, is a good idea because it provides an extra layer of protection should you ever need to bring a copyright infringement suit to court.
Go to the United States Copyright Office online (see resources). Under "How to Register a Work" click on "Electronic Copyright Office." Read the eCO tips, FAQs and tutorials. These will walk you through filing your comic characters and stories.
Create an account with the eCO and fill out the electronic form eCO uses for all types of electronic copyright filing. There will be instructions as you go, but the information you will need is basic. You will fill out the name of the copyright owner, the fact that you're registering a comic for copyright protection, and the date of its creation. This information will be on file should you ever need to log in and retrieve it.
Upload file copies of your work in acceptable file formats. Since you're registering comic characters, you will probably want to upload both text and graphic files. The text file might be a short bio of the character, a description of the character's powers, secret identity, etc. The image files you upload will be your sketches of the characters. If you have a comic storyline as well, you will include that in the registration.