This book can be downloaded and read in Apple Books on your Mac or iOS device.
The theory of relativity, or simply relativity in physics, usually encompasses two theories by Albert Einstein: special relativity and general relativity.  (The word relativity can also be used in the context of an older theory, that of Galilean invariance.)
This isn’t even a book
Waste of time
If you want to read it... don't get this.
Spam. Only 5 pages long with links to external audio files.
Avoid. There is another Relativity eBook at the iBook store which contains the actual book.