Copyright protects digital works like websites the same as physical works like books. As soon as a work of sufficient originality is fixed, it is automatically protected for the life of the author plus 70 years.
As soon as it is "fixed in a tangible medium," it's automatically protected. If formal registration is available in your country, you may wish to do so, although it is not required.
Software is protected by both patent and copyright laws. It's most apparent in preventing copying and distribution of protected applications, and is evident in the small print in EULAs.
Everyone. If you're creating materials, copyright protects your rights to your intellectual property. If you're using materials, copyright limits what you can do with them.