Question

Why did Siddhartha come to be called the Buddha? Where did he give his first sermon?​

Answer 1

At that point he became known as the Buddha (the Awakened or the Enlightened). The Buddha preached his first sermon at the city of Benares, most holy of the dipping places on the River Ganges; that sermon has been preserved and is given here. It reflects the Buddha's wisdom about one inscrutable kind of suffering.

Answer 2

One day, seated beneath the Bodhi tree (the tree of awakening) Siddhartha became deeply absorbed in meditation, and reflected on his experience of life, determined to penetrate its truth. He finally achieved Enlightenment and became the Buddha.