The full title of the philosophy is 'Advaita Vedanta'.   'Vedanta' simply means that it derives from the scriptures that form the last part of the Vedas, the four sacred texts of the Hindu religion.  The literal meaning is 'the end of knowledge', in the sense of being the highest knowledge one can attain.  It is not itself a religion, however—there are no churches or priests.  The first part of the Vedas does contain rituals and so on but Advaita does not itself rely on these.

Advaita is an extremely simple philosophy. Its complete essence is summed up in its Sanskrit name: a - not, dvaita - two.  In a very real sense, there is no need for a book to explain it.  It can be summed up in a single sentence.

            There are not two things.