Just as a single force in space can be mathematically conceived as having various spatial components, the Supreme Being or God, the personal form of the Ultimate Reality, is conceived by Hindus as having various aspects. A Hindu deity represents a particular aspect of the Supreme Being. For example, Saraswati represents the learning and knowledge aspect of the Supreme Being. Thus, if a Hindu wants to pray for acquiring knowledge and understanding, he prays to Saraswati. Just as sunlight cannot have a separate and independent existence from the sun itself, a Hindu deity does not have a separate and independent existence from the Supreme Being. Thus, Hindu worship of deities is monotheistic polytheism and not simple polytheism.
Hindus view cosmic activity of the Supreme Being as comprised of three tasks: creation, preservation, and dissolution and recreation. Hindus associate these three cosmic tasks with the three deities, Brahma, Vishnu and Shiva. Lord Brahma brings forth the creation and represents the creative principle of the Supreme Being. Lord Vishnu maintains the universe and represents the eternal principle of preservation. Lord Shiva represents the principle of dissolution and recreation. These three deities together form the Hindu Trinity.
One must clearly understand that Brahma, Vishnu and Shiva are not three independent deities. They represent the same power, but in three different aspects. Just as a man may be called a doctor, father or husband based upon the tasks he performs, the Supreme Being is called Brahma, Vishnu or Shiva when conceived as performing the three different cosmic tasks of creation, preservation, and dissolution and recreation. "The oneness of the three gods Brahma, Vishnu and Shiva is brought out by the mystic symbol AUM where 'A' represents Vishnu, 'U' Shiva and 'M' Brahma."
Hindu religion is often labeled as a religion of 330 million gods. This misunderstanding arises when people fail to grasp the symbolism of the Hindu pantheon. According to the Hindu scriptures, living beings are not apart from God, since He lives in each and every one of them in the form of atman. Thus each living being is a unique manifestation of God. In ancient times it was believed that there were 330 million living beings. This gave rise to the idea of 330 million deities or gods. Actually, this vast number of gods could not have been possibly worshipped, since 330 million names could not have been designed for them. The number 330 million was simply used to give a symbolic expression to the fundamental Hindu doctrine that God lives in the hearts of all living beings.
Here we present the philosophical concept of God in Hindu dharma.
While Hindus worship God that has a form, where as one without a form, there is a synergy in this apparent contradiction. This is presented in the Saguna and Nirguna Brahman sections.
Thats why Hindu believe in multiple Gods and these concept in reality do not differ from one another.