What is niyat(or neeyat) karma that Gita talks about ?

Lord krishna tells about niyat karma (the prescribed or ordained action that needs to be done) in sloka 8 of chapter 3.
           niyatam kuru karma tvam, karma jyayo hy akarmanah
           sarira-yatrapi ca te, na prasiddhyed akarmanah
                                    -B.G.CHAP3 SLOKA 8
English Translation-“You ought to do your prescribed action as enjoined by scripture, for doing work is better than not doing any, and in the absence of it even the journey of your body may not be completed.’’


Arjun is prompted to do the prescribed action-the ordained task which is distinct from all other kinds of work. Performance of this action is preferable to inaction, because if we do it and traverse even a small part of our way, it can rescue us from the great fear of birth and death. Performance of one’s spiritual duty - the ordained action- is, therefore, the better course. By not doing it we cannot even complete the journey of our Soul through different bodies. Here the prescribed action or niyat karma is such that will free one from the tetacles of birth and death. But what is the prescribed or ordained work that needs to be done ? This is described in the next sloka...
          yajnarthat karmano ’nyatra, loko ’yam karma-bandhanah
        tad-artham karma kaunteya, mukta-sangah samachara
                                   -B.G.CHAP-3-SLOKA 9
English Translation-“Since the conduct of yagya is the only action and all other business in which people are engaged are only forms of worldly bondage, O son of Kunti, be unattached and do your duty to God well.’’

Contemplation of God is the only real action. That conduct is action which enables the mind to concentrate on God. It is a prescribed act and, according to Krishn, tasks other than this are only forms of worldly bondage. Anything other than the performance of this yagya is a form of slavery rather than action. It is important to remind ourselves once more of Krishn’s injunction to Arjun that he shall be freed from the evils of this world only by doing the one real work. The accomplishment of this work, of yagya, is action; and Arjun is urged to do it well in a spirit of detachment. It cannot be performed without disinterest in the world and its objects.

So the conduct of yagya is action.


 But another question that now arises is what this worthwhile act of yagya is ? 


Where does yagna come from and what does it give?