Everything we know about tao-chia Taoism, its concepts and ideas, come from the text of Tao-te ching (The Classic of Tao and Te) ascribed to Lao-tzu.
This book explains what is Tao (the central philosophical item of tao-chia) and what should be the Taoist disciple's conduct in order to follow the Tao, which is his /her main goal.
Chuang-tzu further developed the ideas of Tao-te ching by means of short stories, most of them fictitious, parables and metaphors. There's also the Lieh-tzu classic on the Emptiness and the story of Yang-tzu which added more materials to the already basic stratum of the Taoist works.
We may also count among these sources the well-known I-ching (Classic of Changes), used as oracular means from the ancient times of Chou dynasty. I-ching includes the Taoist philosophy contained in its insights and advices.