Copyright, literally, is “the right to copy.” It guarantees the authors of creative works–including books, artworks, films, recordings, and photographs–the exclusive right to allow others to copy and distribute the work, by whatever means and in whatever media currently exist. It also prohibits copying and distributing without the author’s permission, and includes moral rights: the right of attribution (the right to be named as the creator of the work) and the right of integrity (the right to control changes to the work).
In countries that are signatory to the Berne Convention,, the international source for copyright law (including the USA, Canada, the UK, Europe, and many other countries), you own copyright, automatically, as soon your work is fixed in tangible form–i.e., the minute you write the words. Your ownership extends beyond your death--between 50 and 70 years, depending on which country you're in.
Contained within copyright is the entire bundle of rights that authors can grant to others or utilize themselves. For book authors, that includes primary rights (the right to publish in print and digital formats) and subsidiary rights (the right to make translations and audio recordings and films, to create serializations or abridgements or derivative works…the list goes on, and continues to expand as technology makes different forms of publication and distribution possible).