Short answers, pulled from the story.
The Bhavacakra, or wheel of life, is a visual teaching aid and meditation tool representing samsara, the cycle of cyclic existence and rebirth. It is found on the walls of Tibetan Buddhist temples and monasteries in the Indo-Tibetan region. The image consists of four concentric circles held by Yama, the lord of death, with the Buddha pointing to the moon to represent the possibility of liberation.
The pig, snake, and bird at the center of the Bhavacakra represent the three poisons of ignorance, aversion, and attachment respectively. The pig stands for ignorance because it was considered the most foolish of animals in Indian tradition. The snake represents anger because it strikes at the slightest touch, and the bird represents attachment due to its deep bond with its partner.
The six realms are the god realm (Deva), demi-god realm (Asura), and human realm (Manusha) in the upper half, and the animal realm (Tiryagyoni), hungry ghost realm (Preta), and hell realm (Naraka) in the lower half. The human realm is considered the most suitable for practicing the dharma because humans experience enough suffering to motivate practice without being completely overwhelmed. Buddhist cosmology describes eighteen different types of hells, each inflicting different torments.
Legend credits the historical Buddha with designing the first Bhavacakra. The story of how he gave the illustration to King Rudrayana appears in the Divyavadana, an anthology of Buddhist narratives. The opening paragraphs of the Sahasodgata-avadana section describe the Buddha's specific instructions for creating the diagram.
The outer rim's twelve sections represent the Twelve Nidanas, the causal links of dependent origination, beginning with ignorance and ending with old age and death. Each link is paired with a visual symbol, such as a blind person walking for ignorance, a potter shaping a vessel for volitional activity, and a corpse being carried for aging and death. These links can be read across multiple lifetimes or as operating within a single moment of existence.
The fearsome figure holding the wheel is Yama, the lord of death, and he represents impermanence. His crown of five skulls represents the impermanence of the five aggregates, his third eye symbolizes the wisdom of understanding impermanence, and his four limbs clutching the wheel stand for the four sufferings of birth, old age, sickness, and death. The tiger skin hanging beneath the wheel symbolizes fearfulness.