Buddhists believe that there are three things that end up poisoning our minds, leading to frustration, disillusion, anger, and disppointment. Those three things are ignorance, hate, and greed.
The way to overcome these baser human impulses is to purify the mind. As you might imagine, this is not an easy task, and the path to "enlightenment" is not an easy one. "Enlightenment," to put it very reductively, is state in which an individual has overcome both suffering and desire. It is a difficult thing to divest oneself of selfish interests and corporeal pleasures.
Perhaps the first obstacle to contend with among these three is ignorance. In Buddhism, ignorance is defined as being unaware of the interconnectedness of all things. There is no "I" or "we," no "me or "mine." When this has been understood by the individual, the "thirst" for sensory pleasure is quashed. The way you eliminate ignorance is through meditation. Prince Guatama Siddhartha, the founder of Buddhism said, "Meditation brings wisdom; lack of meditation leaves ignorance. Know well what leads you forward and what holds you back, and choose the path that leads to wisdom."
Once the veil of ignorance is lifted, hatred dissipates. You cannot hate what is a part of you, and all things are connected.
Overcoming greed can happen when "five basic moral precepts" of the spiritual path are adhered to. These principles include the mildest, consuming intoxicants, to the most morally heinous, taking a human life. The other three are stealing, dishonesty, and sexual misconduct.
Of course, it is hard to summarize an entire religion (although to call Buddhism a religions is a misnomer. Buddhism is a life philosophy. There are no gods) in just a brief answer, but the these are its basic tenets.