The Wheel of Life is a symbolic representation of samsara and nirvana.  It shows how, from the first link of ignorance up to the twelfth link of death, beings cycle in samsara through the twelve links.  Who cycles?  By what cause?  Where do they cycle?  How to do they cycle?  How long do they cycle? From when did they cycle?

Each question is addressed in Precious Teachings, by Khenpo Karten Rinpoche, page 52 in print version (58 in PDF version), “Essence of Buddhism as Related to the Four Noble Truths.” 

Image:  This is a painting on the wall of Gaden Tharpa Choorling Gompha, Monastery at Kalimpong, West Bengal, India. Source:  Wikimedia.