The main point of Buddhism is escaping Samsara, though the exact means and method vary according to the school, as do explanations of what happens when you finally accomplish that goal. However, it seems pretty universally agreed upon that the mechanism for remaining in samsara comes down to the twelve nidānas, translated variously as the twelvefold chain or the twelve causal link. These begin with ignorance and progress to birth and “all the sufferings.”
A passage from The Lotus Sutra explains the Links this way:
Conditioned states are dependent on ignorance. Consciousness is dependent on conditioned states. Name and form are dependent on consciousness. The six sense fields are dependent on name and form. Contact is dependent on the six sense fields. Feelings are dependent on contact. Craving is dependent on feelings. Grasping is dependent on craving. Becoming is dependent on grasping. Birth is dependent on becoming. And old age, sickness, death, anxiety, sorrow, suffering, and distress are all dependent on birth.
However, remember that Buddhism is about escaping all that suffering. The next paragraph in The Lotus Sutra says:
When ignorance ceases, then conditioned states cease. When conditioned states cease, then consciousness ceases. When consciousness ceases, then name and form cease. When name and form cease, then the six sense fields cease. When the six sense fields cease, then contact ceases. When contact ceases, then feelings cease. When feelings cease, then craving ceases. When craving ceases, then grasping ceases. When grasping ceases, then becoming ceases. When becoming ceases, then birth ceases. When birth ceases, then old age, sickness, death, anxiety, sorrow, suffering, and distress cease.
This probably sounds fairly grim to non-Buddhists; the bit about all the sufferings of life being due to birth is part of what has gained Buddhism a reputation as nihilistic. (I have been called a nihilist to my face by ill-informed and ill-mannered strangers who did not mean it as a compliment.) However, what lies beyond Samsara is not annihilation but Nirvana…whatever that means.