When the Buddha sat under the tree he focused on his breath. When one focuses on the breath for a period of time, and is well practiced - eventually all thoughts in the mind stop.
Though it might seem a very unnatural state of mind, in Buddhism this is part of the goal because once the thoughts stop churning about in the mind - the mind becomes more aware, free, and responsive without the memories of the past or the hope of the future enchaining it.
Buddhism is the study of what Buddha did to free the mind from suffering. Buddha gave a lot of talks to help people come to the same state of being that he attained - and many have since then. They too are said to be arahants or "Buddhas" but, really the first Buddha is the one that was referred to and is referred to as "Buddha". Others were said to have attained arahantship.
Buddhism in Thailand is practiced a couple different ways. Thai Buddhism follows the Theravada style of Buddhism and yet there are a couple of schools of training.
Some Theravadans believe that one need only sit and meditate in order to attain enlightenment. Others believe you must also add "mindfulness" of the present moment
