This is the understanding that any phenomenon 'exists' only because of the 'existence' of other phenomena in a fabulously complex web of cause and effect covering time past, time present and time future. This concept of a web is symbolised by Indra's net (also called Indra's jewels or Indra's pearls, the term is a metaphor used to illustrate the concepts of emptiness, dependent origination interpenetration in Buddhist philosophy), a multi-dimensional spider's web on which lies an unnumbered amount of dew drops or jewels, and in these are reflected the reflections of all the other drops of dew infinitely.
Stated in a different way, everything depends on everything else. For instance, a human being's existence at any given moment is dependent on the condition of everything else in the world (and indeed the universe) at that moment but, on the contrary, the condition of everything in the world in that moment depends in an evenly substantial way on the character and condition of that human being. Everything in the universe is interlinked through the web of cause and effect, so that the whole and the parts are mutually interdependent. The character and condition of entities at any given time are closely connected with the character and condition of all other entities that apparently may appear to be unconnected or unrelated.
As all things are thus conditioned and transitory (anicca), they have no real independent identity (anatta), so do not truly 'exist', although to average minds this appears to be the case. All phenomena are thus basically unsubstantial and 'empty' (sunya).
Human beings with a wise bent of judgement, who 'see things as they are' (yatha-bhuta-ñana-dassana), relinquish attachment and clinging, transform the energy of desire into awareness and understanding, and ultimately transcend the conditioned realm of form, becoming Buddhas or Arhats.
Buddha found two ways to apply the concept of dependent origination. One was the Four Noble Truths and the other was the Twelve Nidanas. The Four Noble Truths will lead one to the Eight fold Paths, which will be instrumental in achieving arahantship and nirvana. Twelve Nidanas is the conditional existence that propagates the theory of that the three stages of life of a being (past, present and future) are dependent on each other. One's actions will decide the fate of the next stage of his life.
The postulates of birth and death are based n dependent origination. Without birth there can be no death. So what living beings view as life is again conditioned by attachments and wealth. Buddha realized that the craving in humans is related to senses and to free oneself from this web of dependent origination it was vital to conquer the senses. It was necessary to overcome this psychophysical phenomenon for a dukkha free life.
Dependent origination in Buddhism, thus, became a primary pillar on which some of the most important Buddhist doctrines were based.