The Buddha’s first Sutra or Sutta
As I present various Sutras, I will give a brief explanation, a link or two to Wikipedia for more information and also a link to an online version, if available. As I have stated many times the Buddha taught us to test everything, and adopt it if we find it useful, and does not cause harm to any being. If you still have questions, perhaps see if there is a Temple or Wat close enough for you to visit. Many also offer retreats to the public, where you may learn meditation or receive further education in Buddhism.
The first Sutra I will mention is the one that all schools of Buddhism agree on. It was the lesson he taught to the five ascetics who he met again shortly after becoming enlightened. These five ascetics who listened to his discourse in Deer Park, Sarnath, became his first disciples, This is also referred to as the original or first turning of the Dharma wheel.