From pbs.org, a commentary on the Four Noble Truths of Buddhists:
The Four Noble Truths comprise the essence of Buddha's teachings, though they leave much left unexplained. They are the truth of suffering, the truth of the cause of suffering, the truth of the end of suffering, and the truth of the path that leads to the end of suffering. More simply put, suffering exists; it has a cause; it has an end; and it has a cause to bring about its end.
The notion of suffering is not intended to convey a negative world view, but rather, a pragmatic perspective that deals with the world as it is, and attempts to rectify it.
The concept of pleasure is not denied, but acknowledged as fleeting. Pursuit of pleasure can only continue what is ultimately an unquenchable thirst. The same logic belies an understanding of happiness. In the end, only aging, sickness, and death are certain and unavoidable.
The Four Noble Truths are a contingency plan for dealing with the suffering humanity faces -- suffering of a physical kind, or of a mental nature.
The First Truth identifies the presence of suffering. The Second Truth, on the other hand, seeks to determine the cause of suffering. In Buddhism, desire and ignorance lie at the root of suffering. By desire, Buddhists refer to craving pleasure, material goods, and immortality, all of which are wants that can never be satisfied. As a result, desiring them can only bring suffering.
Ignorance, in comparison, relates to not seeing the world as it actually is. Without the capacity for mental concentration and insight, Buddhism explains, one's mind is left undeveloped, unable to grasp the true nature of things. Vices, such as greed, envy, hatred and anger, derive from this ignorance.
The Third Noble Truth, the truth of the end of suffering, has dual meaning, suggesting either the end of suffering in this life, on earth, or in the spiritual life, through achieving Nirvana.
When one has achieved Nirvana, which is a transcendent state free from suffering and our worldly cycle of birth and rebirth, spiritual enlightenment has been reached.
The Fourth Noble truth charts the method for attaining the end of suffering, known to Buddhists as the Noble Eightfold Path. The steps of the Noble Eightfold Path are Right Understanding, Right Thought, Right Speech, Right Action, Right Livelihood, Right Effort, Right Mindfulness and Right Concentration. Moreover, there are three themes into which the Path is divided: good moral conduct (Understanding, Thought, Speech); meditation and mental development (Action, Livelihood, Effort), and wisdom or insight (Mindfulness and Concentration).