The Essence of the Four Noble Truths

Shortly after attaining enlightenment under the bodhi tree, the Buddha gave a sermon in Varanasi sharing the fruits of his realization. This sermon is referred to as the "first turning of the wheel of Dharma." The word Dharma here refers to the Buddha's teachings themselves. It was this sermon in which the Buddha developed what would become the framework for the entirety of his teachings: the four noble truths.
These four truths are the truth of suffering, the truth of its origin, the truth of the possibility of its cessation, and the truth of the path that leads to that cessation. In essence, the four noble truths say that we all naturally desire happiness and do not wish to suffer--and that the suffering we wish to avoid comes about as a result of a chain of causes and conditions begun even before our birth. If we are to pursue our aspiration to gain freedom from suffering, we need to clearly understand the causes and conditions that give rise to suffering and strive to eliminate them. Additionally, we must clearly understand the causes and conditions that give rise to happiness as well, and actively practice them. This is the essence of the four noble truths.
--from Essence of the Heart Sutra: The Dalai Lama's Heart of Wisdom Teachings by H.H. the Dalai Lama, translated & edited by Geshe Thupten Jinpa