The wheel of life shows the six spheres of existence within which sorrowful lives take place and to which a man is chained by desire, ignorance and hatred. The circle is held by demon ~ Yama indicating lives must die and live again. 

The outer circle of the wheel shows 12 links in the chain of causation which binds living beings to the misery of inner circle and six world of ~

1 Gods symbolizes the life of comfort, pleasure and apparent immorality which leads to pride and self assurance.

2 Titans or semi gods is that of suffering caused by perpetual strife due to envy.

3 Human realms are marked by the suffering of sickness, old age and death caused by desire or passion.

4 Animal worlds symbolize lethargy and spiritual incapacity of life governed by instincts.

5 Spirit symbolizes the suffering through permanent hunger caused by greed and avarice.

6 Hell is that of suffering of fiery heat and icy cold caused by hatred and anger. 

Twelve sections of Outer ring are

1 Death shown by a man carrying on his back a corpse to the funeral prey.

2 Birth shown by birth scene.

3 Becoming is shown by union of husband and wife.

4 Appropriation is shown by a man picking fruit from a tree and storing it.

5 Desire is shown the form of man drinking wine.

6 Feeling is shown by an arrow entering a man's eye.

7 Contact is shown as an embrace between lovers.

8 Senses are represented by a house with six windows.

9 Personality is shown by a boat with two persons.

10 Consciousness is shown by a monkey climbing a tree,

11 Elemental impulses are shown by the pots which a potter shapes from clay.

12 Ignorance is represented by blind women led by a stick. 

As a spontaneous search back into the origin of death and rebirth, the ultimate cause of which is ignorance, which stimulates desires and maintains self propelling of existence.