Short answers, pulled from the story.
The word bhavachakra combines two Sanskrit terms: bhava meaning being or worldly existence, and chakra meaning wheel. Monier Monier-Williams published his Sanskrit English Dictionary in 1899 to define these roots.
Legend states the historical Buddha created the first depiction of this symbol. The story appears in the Divyāvadāna anthology within the Sahasodgata-avadāna section where the Buddha instructed King Rudrāyaņa to create the illustration.
Three animals occupy the center hub of the painting: a pig, a snake, and a bird. These creatures represent ignorance, aversion, and attachment respectively while forming a cycle of mutual reinforcement.
Propelled by their karma, beings take rebirth in six distinct realms of samsara. Three higher realms include gods enjoying pleasure but lacking practice, demi-gods fighting constantly, and humans facing hunger and sickness. Three lower realms feature animals fearing predators, hungry ghosts with huge bellies and thin necks, and hell beings enduring eons of torment.
The outer rim divides into twelve sections representing the Twelve Nidānas which show how past lives influence current lifetimes and future ones. A blind person walking represents lack of knowledge or avidyā while a potter shaping vessels illustrates constructive volitional activity called sañskāra.
A fearsome figure holds the wheel representing impermanence and this entity is often identified as Yama lord of death or Mara the demon who tempted Buddha. He wears a crown of five skulls symbolizing the impermanence of the five aggregates.