Not a lawyer either. Characters may be protected by copyright, in as much as their manifestations in writing, or visual depictions etc. is protected by copyright, and copyright includes the right to control derivative works.

So if I describe a young boy that goes to wizard school in a book, then that idea is not protected by copyright, but if the way I describe him makes him similar enough to Harry Potter, I would risk that a court would determine that the character is a derivative work and find copyright infringement.

Trademark can also apply, if the characters have been used in association with products, but not generally for the work itself.