The Prince Siddhartha Gautama had been raised in luxury, carefully protected from all discomfort by his doting father. While traveling outside the palace, however, Siddhartha saw three very troubling sights: an old man, a sick man, and a corpse. Despite the best efforts of his father, the prince had become aware of suffering.
It took more than six years, but Siddhartha finally became enlightened--the Buddha. In his first sermon, he taught the Four Noble Truths.

Dukkha

The first is the truth of Dukkha, the understanding of suffering. Everyone suffers. However, most of us do not understand our suffering--we go through stress without knowing our stress. The Buddha explained there are two classes of Dukkha.
1. First, there is the state of permanent suffering. Birth is suffering, from the time of conception to delivery; aging is suffering, and death is suffering.
2. Second, there is impermanent suffering: sorrow, lamentation, pain, grief, despair, the suffering that comes from having something unpleasant; the suffering that comes from being separated from loved ones; the suffering that comes from not having what one wants.

Samudaya

The second truth is that of origin--the sources of suffering. Suffering is caused by craving: the craving to have something; the craving to be something; and the craving to not be something--to not be old, to not be sick, and so on.

Nirodha

The third truth is that of cessation of dukka. We tend to labor under the misconception that when the stress is lessened--when the situation surrounding dukkha ceases, that the suffering will end: "If only I wasn't so broke! If I get a raise, I'll be happy." However, the Buddha recognized that changing the situation --the physical elements -- doesn't end suffering. The only way to eliminate suffering was to change one's mind. When one ends all defilments, all attachments, all aversions, one ends suffering.

Magga

The fourth noble truth is the Eightfold Path, the Middle Way: Right view; right resolve; right speech; right action; right livelihood; right effort; right mindfulness; right concentration.