Socrates left no writings, but we know of his teachings through the works of his pupil Plato, who presented many of his works in the form of Dialogues in which Socrates was the main speaker, though it is probable that many of the ideas that are put into his mouth are those of Plato.
Socrates is also mentioned in works of his contemporary Xenophon, and was satirised as a sophist in plays of Aristophanes.
Socrates taught by the Socratic Method of getting people to say what they thought and then questioning them and revealing inconsistencies.
He proved to be too successful in getting young men to think for themselves, so that they started to dispute with their elders. He was charged by the elders with leading youth astray, and sentenced to die, by drinking hemlock. He is often thought of as a martyr of rationalism.