Copyright protects the physical expression of ideas. As soon as an idea is given physical form, e.g. a piece of writing, a photograph, music, a film, a web page, it is protected by copyright. There is no need for registration or to claim copyright in some way, protection is automatic at the point of creation. Both published and unpublished works are protected by copyright.
Copyright is normally owned by the creator(s) of the work, e.g. an author, composer, artist, photographer etc. If the work is created in the course of a person's employment, then the copyright holder is usually the employer.
Copyright is a property right and can be sold or transferred to others. Authors of articles in academic journals, for example, frequently transfer the copyright in those articles to the journal's publisher. It is important not to confuse ownership of a work with ownership of the copyright in it: a person may have acquired an original copyright work, e.g. a painting, letter or photograph, but unless the copyright in it has expressly also been transferred, it will remain with the creator.