In plain words
Various countries have been divided into two categories -- the 'land of karma' and the 'land of enjoyment' -- and something of the ideals of their peoples has also been told regarding this. Among these, it has been determined that the land of Bhārata is the land of karma, and that it has recognized the secret of karma well. '"Vyāpāra" verily is karma' -- this is of two kinds, worldly and Vedic. Among these, all karma that becomes the very cause of life is called worldly. Vedic karma is of two kinds, śrauta and smārta. The daily rites, the occasional rites and the like, smārta karma, and all worldly and Vedic karmas together are of three kinds because of the instrument used -- mental, verbal and bodily. These, further, are of two kinds: done in a previous birth, and done in this present birth. Its fruits alone are of three kinds: sañcita, āgāmi and prārabdha. What is experienced in this birth is prārabdha; what is being done now is āgāmi; and what has been accumulated from many births and stands waiting for future experience is sañcita. Thus the whole system of karma, and the entire working of karma, have been determined by the Śruti and the Smṛtis. The word 'karma' is very small; even so, it is boundless in the abundance of its meaning. Each person may define for themselves the meaning of this word 'karma', according to their own respective intellect.
This karma occurs through the three instruments -- mind, speech and body. The entire connection of worldly, Vedic and transcendental matters is contained in this very karma.