The Nature of Brahman
Brahman is the basis, source and support of everything in the cosmos (Brahmanda). Its nature is Absolute Being (sat), Consciousness (chit), and Bliss (ananda). Brahman is eternal, infinite, formless, all-embracing, and everything that ever was, is now, or ever will be. Brahman is the Ultimate Reality.
Using mere words to define a concept as vast and complex as Brahman is bound to fail; therefore, Hinduism has developd a reductive device to help us approach and feel connection to that which cannot be comprehended in its entirety.
First, the principle of Brahman is divided into two realities; Brahman itself – eternal, absolute, the ultimate reality. And Maya, our perceived reality which in fast is an illusion living, dying and being reborn on the wheel of time (samsara).
The second reductive device is the concept of Brahman divided into aspects deemed male (Purusha) and female (Prakriti), personified as individual gods and goddesses, each with their particular set of responsibilities and temperament, and each embodied in a unique human-like physical form (note 1). For example, when Shiva embodies the Purusha principle, it is Uma who embodies the Prakriti.
“Ye yatha mam prapadyante tanstathaiva bhajamyaham.”
“I come to you in whatever form you worship Me.”
Bhagavad Gita 4:11
Generally speaking, deities such as Uma, Shiva or Vishnu are not divine in their own right – and here is an important point – they are specific physical manifestations of Brahman (note 2). A metaphor might be Brahman as a vast cosmic diamond, and individual gods and goddesses as facets of that diamond rather than individual diamonds.
Note 1 – Gods and goddesses exist on a higher plane in formless state and leave that plane to inhabit human form only when a physical body is required by us mortals for worship or to deal with a problem such as a demon, for example.
Note 2 – Followers of sects such as Saivites or Vaisnavites (the Great Gods, or Mahadevas) or Shaktics (the Great Goddesses), however, may argue their chosen god or goddess is Supreme over all other concepts or manifestations of Brahman.