What is not protected by copyright?
Ideas are not protected by copyright, only the expression of them. To make this distinction clear, it is worthwhile to consider an example of this:
An author writes a book describing electric vehicles that includes diagrams, technical drawings, and sufficient information to understand how to construct an electric vehicle. The author owns copyright over the specific description of the car, images/drawings they created, and of the book as it is written. The author does not, however, own the invention of the electric car or the ideas presented in the book.
If someone were to read this book, they would be free to use the ideas presented to design their own electric vehicle or write their own book on the subject. To avoid infringement, they must not copy specific passages or images from the book. They should also ensure that any material they create is sufficiently unique so as not to be considered a derivative work, even if accidentally.
Additionally, works that have not been fixed remain as ideas and therefore cannot be copyrighted. For example, someone spontaneously invents and performs a dance routine. It is not eligible for copyright unless the routine was also recorded in some way.
Furthermore, facts (such as mathematical formulae); commonly known information (such as standard calendars); or names, short phrases, or titles; cannot be copyrighted.