COPYRIGHT FOR NEWSPAPERS

Hi! I've had some success having Op-Eds and letters published by the Providence Journal, unpaid as of this time. I know that the newspaper has the right to alter my material, and to republish it in other venues. I want to know what rights I retain to my Op-Eds and letters. Can I republish in other journalistic venues? Can I publish in a book? I believe I can upload my material on my own site. If someone would inform me about newspaper copyright, and give me a few links, I would appreciate it. Thanks. Ted