Simplify the following text for a Grade 6 native English-speaking person.
Original: According to the Pali Tipitaka and the Ä gamas of other early Buddhist schools , the Four Noble Truths were the first teaching of Gautama Buddha after attaining Nirvana . They are sometimes considered to contain the essence of the Buddha 's teachings :
Simplified: The Buddha 's first and most important teachings are the Four Noble Truths .