"Oṃ namo bhagavate Vasudevāya"
Lord Viṣṇu, preserver of all the worlds. He lives outside logic, outside material, he is the one, to whom the materialism is subservient. He is also known as Nārāyaṇa, Hari, Acyutānaṅda, Aniruddha etc. His abode is Vaikuṅṭha dhāma, a place where the human soul is out of all miseries of life, where the soul is free of the cycle of life and death, the place of eternal bliss. He is depicted as lying on a huge serpent known as Śeṣanāga or Ādiśeṣa(represents time) who is also capable of taking avatāra, famously Lakṣamaṇa in Rāmāyaṇa, and Balarāma in Mahāṃbhārata, his consort is Goddess Lakṣmi, the Goddess of wealth and fortune who is massaging Lord Viṣṇu's legs or is always sitting near his feet. Lord Viṣṇu has four arms, he is dark in appearance, depicted blue, in his upper right hand, he holds a Cakra(Sharp circular golden blade), also known as Sudarśana Cakra, in his upper left hand, he holds a Śankha(A blowing intrument), his lower right hand holds a golden mace and lower left hand holds a lotus flower. All around the serpent bed is ocean of milk or Kṣira sāgara. His vehicle is a bird Garūḍa.
Lord Viṣṇu creates a Brahmā as he exhales and when he inhales, he takes in a Brahmā. The universe we live in is one of those Brahmā's, and it will end in a very long time but for Lord Viṣṇu, it is merely an inhale.
In Vaiṣṇavism, Lord Viṣṇu is depicted as the Supreme deity. There is a very deep thing about Lord Viṣṇu and Lord Śivā, that both of them are submissive to each other.
According to Vaiṣṇnav traditions, Lord Viṣṇu created time, all the worlds float around him as if necklace of pearls, "mayi sarvam idaṁ protaṁ sūtre maṇi-gaṇā iva."
Whenever the dharma is on the verge of end, Lord Viṣṇu takes birth as an avatāra on all the worlds to re-establish the dharma. He usually takes birth at the end of an era or in between. One of his avatāra was Lord Sugāta Buddha(Not Siddhartha Gautama)and the upcoming avatāra is Kalkī, who would appear at the end of Kaliyuga(present era, era of machines), nearly 4,27,000 years later.
Lord Viṣṇu's most prominent avatāras are Lord Rāma and Lord Kṛṣṇā. Lord Rāma is known as Maryādā puruṣottama and Lord Kṛṣṇā is known as Māyā puruṣottama.
Just like Lord Śivā is the destroyer, Lord Viṣṇu is also the destroyer, according to Vaiṣṇavism, as his exhale and inhale creates and destroys universes or worlds.
Lord Viṣṇu came from Āryans and thus is less followed in South India. He is equivalent of Lord Śivā.