Lord Vishnu is the God of preservation in the Universe preserving and sustaining the Universe.
The four arms of the lord signify his omnipresence and omnipotence.

The two front arms indicate the lord's activity in the physical world and the two back arms represent his activity in the spiritual world.

The right side of the body represents the creative activities of the mind and the intellect. The left side symbolizes the activities of the heart which are love, kindness, and compassion. The conch in the upper left hand indicates that the Lord communicates with His devotees with love and understanding.

The chakra in the upper right hand is for the protection of his devotees from evil. The mace in the left lower hand signifies that he sustains the manifest world through the energy which he holds in Himself.

The front right hand bestows grace on his devotees.

The thousand heads of the snake signify innumerable desires and passions of an individual.

The lord sitting on the coils of the snake represents that the Lord has controlled all desires.
The blue sky in the background suggests that he pervades the entire universe infinitely.

He is referred as the nameless, the formless, and the immeasurable.

The yellow clothes of the Lord signify that he incarnates Himself on this earth to uphold righteousness and destroy evil and unrighteousness.

The flower garland around the neck is a symbol of the devotee's adoration for the Lord.

The gem symbolizes that the Lord fulfills all genuine desires of his devotees.

The crown represents the supreme power and the authority.

The two earrings signify the dual nature of knowledge and ignorance, happiness and unhappiness, and pleasure and pain. 

The following ten incarnations of Lord Vishnu are described in Hindu mythology.

Matsya or Fish - This form of Vishnu saves Sage Manu from floods and recovers the Vedas from demons.

Kurma or Tortoise - Through this form, Vishnu sustains the earth on his back.

Varaha or Boar - Vishnu brings the earth back from the bottom of the ocean where it was dragged down by a demon, known as Hiranyaksha killing the demon.

Narasimha or Man-lion - Vishnu kills the demon King Hiranyakashipu, to save his devotee.
 
Vamana or Dwarf - The lord kills the demon King Mahabhali, who had deprived the gods of their possessions.

Parasurama or The warrior with an axe - Vishnu saves Brahmins from the tyranny of the arrogant Kshatriyas.

Rama - Vishnu kills Ravana, the demon king of Lanka and builds Ramarajya.

Sri Krishna - Vishnu in the most popular incarnation has made contributions throughout his life including the teachings of the Bhagavad Gita to Arjuna.

Buddha - He is considered as an incarnation of Vishnu by the Hindus and accept his teachings, but do not directly worship him.

Kalkin or The man on a white horse - This incarnation which is yet to come marks the end of all evil in the world.