Kalpa is the Vedanga concerned with ritual procedures, religious ceremonies, and dharmic conduct. It provides the practical framework for how Vedic knowledge is applied in daily life and sacred ceremonies.
Rules for the great Vedic fire rituals (yajnas) performed with multiple fires. These elaborate ceremonies, some lasting days or weeks, are described in texts like the Apastamba Shrauta Sutra and Katyayana Shrauta Sutra. They form the most ancient layer of Indian ritual practice.
Rules for domestic rituals and the 16 Samskaras (rites of passage) from conception to cremation: Garbhadhana, Pumsavana, Simantonnayana, Jatakarma, Namakarana, Annaprashana, Chudakarana, Upanayana, Vivaha, and Antyeshti among others. These govern the entire lifecycle of a Hindu.
Rules for ethical conduct, social duties, and dharmic living. The Dharma Sutras of Gautama, Baudhayana, Apastamba, and Vasishtha form the foundation of Hindu law and were later expanded into the Dharmashastras (like Manusmriti).
Geometric rules for constructing fire altars (vedis). The Sulba Sutras contain remarkable mathematics: the Pythagorean theorem (predating Pythagoras), methods for squaring the circle, irrational number approximations, and geometric transformations. They represent the earliest known Indian mathematics.