As the author/creator of an original work the copyright belongs to you. This protection is immediate, does not require registration, and lasts for the life of the author + 70 years.
Registration can be beneficial. You may want to consider it if in the future you will want to gaurantee the ability to take someone to court and obtain damages from them for infringing your rights.
The process of publishing often involves authors signing over or transfering their rights to the publisher. When you sign over your rights, you no longer own the material you created. You do have options: