Nārāyaṇa (नारायण) is one of the forms and names of Vishnu. Nārāyaṇa is He who dwells in the primal celestial waters, as well as He who dwells within all human beings. Nārāyaṇa lies in blissful Yogic sleep in the primal waters, dreaming the multiverse into being.
He is the Source and Essence of all. We all abide and have our whole existence within His consciousness, and He abides within us. Ultimately everything is part of Him and nothing is separate. He is the Supreme Being.
“This universe is Nārāyaṇa, the Imperishable, the Supreme, the Goal, multi-headed and many-eyed, the resplendent, the source of delight for the whole universe. This universe is the Purusha; it subsists on That, the Eternal, which transcends the universe, the omnipresent Absolute which destroys all suffering. Nārāyaṇa is the protector of the universe, the Lord of the Self, the perpetual, the auspicious, the indestructible, the Goal of all creation, the Supreme object worthy of being known, the Self of all beings, the Refuge unfailing. The Lord Nārāyaṇa is the Supreme Absolute; Nārāyaṇa is the Supreme Reality; Nārāyaṇa is the Supreme Light; Nārāyaṇa is the Supreme Self; Nārāyaṇa is the Supreme Meditator; Nārāyaṇa is the Supreme Meditation. Whatever all this universe is, whatever is seen or heard of, the Eternal Divine Being stands supreme, pervading all this from inside and outside alike. He is the Limitless, Imperishable, Omniscient, residing in the ocean of the heart, the cause of the happiness of the universe, the Supreme End of all striving, dwelling in the ether of the heart… We bow again and again to the omni-formed Being, the Truth, the Law, the Supreme Absolute, the Purusha of blue color decked in yellow, the Centralized Force, the Power, the All-Seeing One. We commune ourselves with Nārāyaṇa, and meditate on Vasudeva. May that Vishnu inspire our consciousness.” - Krishna Yajur Veda, Taittiriya Aranyaka, Nārāyaṇa Sukta
“He is without birth and death, of radiant splendour, the Creator of the universe and the Lord of all! Indeed, He who is the invisible cause of all, who knoweth no deterioration, who is the all-pervading soul, the centre round which everything moveth, the substance in which the three gunas of Sattva, Rajas and Tamas co-inhere, the Universal Soul, the immutable, the material out of which hath been created this universe, the Creator Himself, the Controlling Lord, the invisible dweller in every object, progenitor of this universe of five elements, who is united with the six high attributes, is the Pranava or Aum of the Vedas, is infinite, incapable of being moved by any force save His own will, illustrious, the embodiment of the mode of life called Sannyasa, who floated on the waters before the creation, who is the Source whence hath sprung this mighty frame, who is the great combiner, the uncreated, the invisible essence of all, the Great Immutable, bereft of those attributes that are knowable by the senses, who is the universe itself, without beginning, birth, and decay, possessed of infinite wealth. That Grandsire of all creatures became incarnate in the race of the Andhaka-Vrishnis for the increase of virtue.” - Mahabharata, Adi Parva
“I am Nārāyaṇa, the Source of all things, the Eternal, the Unchangeable. I am the Creator of all things, and the Destroyer also of all. I am Vishnu, I am Brahma, and I am Shankara, the chief of the Devas. I am Raja Vaisravana, and I am Yama, the lord of the deceased spirits. I am Shiva, I am Soma, and I am Prajapati Kashyapa. And… I am he called Dhatri, and he also that is called Vidhatri, and I am Yagnya embodied. Fire is my mouth, the earth my feet, and the Sun and the Moon are my eyes; the Heaven is the crown of my head, the firmament and the cardinal points are my ears; the waters are born of my sweat. Space with the cardinal points are my body, and the Air is my mind... Whatever is obtained by humans by the practice of truth, charity, ascetic austerities, and peace and harmlessness towards all creatures, and such other handsome deeds, is obtained because of my arrangements. Governed by my ordinance, humans wander within my body, their senses overwhelmed by me. They move not according to their will but as they are moved by me.” - Mahabharata, Varna Parva
According to the Vishnu Mahapurana, Nārāyaṇa is the inherently existent imperishable Brahman; He is Ishvara; He is Purusha; with the three gunas He is the cause of creation, preservation, and destruction; He is the parent of Nature, of consciousness, and all ingredients of the universe. He is Hiranyagarbha, Hari, and Shankara. He is the root of the universe, the support of all things, and the universe consists of Him. He is unborn, imperishable, undecaying, Self-existent. He always exists everywhere, and all things exist in Him; He is all things.
Nārāyaṇa is described by the seers as having the Divine blackish-blue color of heavily water-laden clouds. He has four arms, holding a padma (lotus), the great mace Kaumodaki, the conch shell Panchajanya, and the Sudarshana Chakra (discus). But this form is just for us humans to better connect with. Nārāyaṇa’s true universal form (Vishvarupa) is infinitely beyond the ordinary limits of human perception, comprehension, or even imagination.
Once liberated, we can enjoy infinite bliss for eternity in the company of Nārāyaṇa, and/or merge fully into Him.