Upanishads and Vedas are the most popular and often confusing terms for those who are looking to learn Vedic knowledge and information. Vedas and Upanishads are entirely different compositions. Upanishads are the concluding portions of the Vedas or the end of the Vedas. The teaching based on Upanishads is called Vedanta.
Upanishads and Vedas – Difference
Upanishads are the gist and the goal of the Vedas, The Vedas are the eternal truths revealed by God to the great ancient Rishis. The Rishis saw the truths or heard them. Therefore, the Vedas are what are heard (Sruti). There are 4 Vedas and many Upanishads to each Veda as there are Sakhas, branches or recensions, i.e, 21, 109, 1000, and 50 respectively.
The Vedas are eternal. They are without beginning and end. An ignorant man may say how a book can be without a beginning or end. By the Vedas, no books are meant. Vedas came out of the breath of the Lord. They are the words of God. The Vedas are not the utterances of persons. They are not the composition of any human mind. They were never written, never created. They are eternal and impersonal.
According to Swami Vivekananda, The Gita is a commentary on the Upanishads. The Upanishads are the Bible of India. They occupy the same place as the New Testament does. There are [more than] a hundred books comprising the Upanishads, some very small and some big, each a separate treatise. The Upanishads do not reveal the life of any teacher, but simply teach principles.
Out of 100s of Upanishads, the most important Upanishads are Isa, Kena, Katha, Prasna, Mundaka, Mandukya, Aitareya, Taittiriya, Chhandogya, Brihadaranyaka, Kaushitaki and Svetasvatara and Maitrayani. These are supremely authoritative.
The Veda is divided into four great books: the Rig-Veda, the Yajur-Veda, the Sama-Veda, and the Atharva-Veda. The Yajur-Veda is again divided into two parts, the Sukla and the Krishna. The Krishna or the Taittiriya is the older book and the Sukla or the Vajasaneya is a later revelation to sage Yajnavalkya from the resplendent Sun-God. (Read More)
May the fundamental truths of the Vedas be revealed unto you all, like the Amalaka fruit in the palm of your hand. May Gayatri, the blessed Mother of the Vedas, impart to you the milk of Knowledge, the ancient wisdom of the Upanishads. (source)