The Bhagawan Gita forms a part of the root texts of Vedanta. Krishna gives these teachings to Arjuna and through Arjuna to all of us. If there is one book you should study, if you want to know Hinduism, it is definitely the Bhagavad Gita. Upanishads form part of the Ved as they form the final teachings of the Vedas.
Swami Sarvapriyananda summarizes the first chapter of the Bhagavad Gita. This series of talks unfolds the highest truths of Vedanta through the study of "The song of God".