The Twelve Links of Dependent Origination is the Buddhist analysis of the causes and conditions which lead to life. Each link in the chain is the cause that gives rise to the next link, and each link can be broken by removing the link preceding it. The twelve links are:
Ignorance means lack of light or lack of understanding. In Buddhism, "ignorance" usually refers to ignorance of the Four Noble Truths, in particular that life is suffering(unsatisfactory; stressful).
Ignorance also refers to ignorance of Self, a teaching that there is no "self" in the sense of a permanent, integral, autonomous being within an individual existence. What we think of as our self, our personality and ego, are temporary creations of the five aggregate.
2. Mental formations
Ignorance links to samskara, which can be translated volitional action, formation, impulse, motivation, or karma formation. Out of ignorance come thoughts, words and actions that sew the seeds of Karma. Mental formations are the impulses that come before action, and action creates karma. In the outer ring of the Bhavachakra (Wheel of Life), Mental formation usually is illustrated as potters making pots.
In Buddhist teaching there are many kinds of Consciousness. Very generally, consciousness is what happens when one of the six faculties (eye, ear, nose, tongue, body, mind) reacts to or becomes aware of one of the six external phenomena (visible form, sound, smell, taste, touch, and ideas and thoughts).
4. Name and form
Name and form is name and form, corporeality and mentality, the joining of the five Skandhas into an individual existence. With name and form also come sensory perception.
5. The six sense organs
The consciousness, link described above involves the the six faculties or sense organs (eye, ear, nose, tongue, body, mind) and six corresponding external phenomena, or objects (visible form, sound, smell, taste, touch, and ideas and thoughts). The sense organs do not exist separately from the previous link, physical form. If you reflect on the links, you see that each link connects to every other link.
Sparsha is contact with environment, or the contact with the faculties and object. The contact of faculties and objects leads to the experience of sensation, which is the next link.
Feeling is the recognition and experience of sensations. These experiences are pleasurable or painful, which leads to desire and aversion. Sensation conditions the next link, craving.
The Second Noble Truth teaches that trishna(Craving) -- thirst, desire or craving -- is the cause of stress or suffering (dukkha). If we are not mindful, we are perpetually being jerked around by desire for what we want and aversion of what we don't want. In this state we heedlessly create Karma, which keeps us entangled in the cycle of Rebirth. Desire and aversion conditions the next link, clinging.
We cling to sensual pleasures, mistaken views, external forms and appearances. Most of all, we cling to ego and a sense of an individual self, a sense reinforced moment-to-moment by our cravings and aversions. Clinging also represents clinging to a womb and the beginning of rebirth.
The Wheel of Life illustrates becoming by picturing a couple making love or a woman in an advanced state of pregnancy.
The cycle of rebirth naturally includes birth. In the Wheel of Life, a woman in childbirth illustrates jati.
Birth inevitably leads to old age and death.
12. Aging and death
The chain comes to old age and death, or the dissolution of what came to be. The karma of one life sets in motion another life, rooted in ignorance. A circle is closed.