In
Buddhism, there are two main kinds of
meditation:
metta, also known as
loving-kindness meditation, and
insight meditation.
Metta meditation is used for the purpose of developing a kind of goodwill and respect towards yourself and all other creatures in the universe.
Insight meditation is used for the purpose of developing greater insight (thus, the name) into the true nature of reality and thought. It is the primary tool in Buddhism used to understand the Four Noble Truths.
Please see my entries at Metta and Insight Meditation for information on how to meditate in either of these two fashions.