Bhashya
अधुना दमादिसाधनत्रयविधानार्थोऽयमारम्भः—त्रयाः,त्रिसंख्याकाः प्राजापत्याः प्रजापतेरपत्यानि प्राजापत्याः, तेकिम्? प्रजापतौ पितरि ब्रह्मचर्यं शिष्यत्ववृत्तेर्ब्रह्मचर्यस्यप्राधान्यात् शिष्याः सन्तो ब्रह्मचर्यम् ऊषुः उषितवन्तःइत्यर्थः ।के ते? विशेषतः देवा मनुष्या असुराश्च ।ते चउषित्वा ब्रह्मचर्यं किमकुर्वन्नित्युच्यते— तेषां देवा ऊचुःपितरं प्रजापतिम् ।किमिति? ब्रवीतु कथयतु, नः अस्म-भ्यम् यदनुशासनं भवानिति ।तेभ्यः एवमर्थिभ्यः ह एत-
In plain words
Now the text turns to why these three practices -- restraint and the rest -- are being laid down. 'Three' simply means three in number. 'Prājāpatyāḥ' means Prajāpati's own offspring. And who are they? They lived with Prajāpati their father as students -- disciples first and foremost, since studentship is what discipleship really means -- so 'they dwelt' simply says they had lived through that period. Who, specifically? Gods, men, and demons. And once their studentship was finished, what did they do? Here is the answer: the gods spoke first, to Prajāpati their father. What did they say? 'Won't you tell us, sir, whatever you have to teach?' To them, asking in just this way...
Close to the Sanskrit
Now this undertaking is for the purpose of prescribing the triad of means beginning with restraint -- 'three', that is, numbering three; 'Prājāpatyāḥ' [means] the offspring of Prajāpati [are called] 'Prājāpatyāḥ'. What are they? '[They dwelt] with Prajāpati [their] father in studentship' -- being disciples, because of the primacy of studentship as the very mode of discipleship, they 'dwelt' in studentship, that is, 'had dwelt' -- such is the meaning. Who are they? Specifically, gods, men, and demons. And having dwelt [there], what did they do with their studentship? -- this is now stated: of them, the gods spoke to their father Prajāpati. Saying what? 'May [our] lord speak, may he tell us whatever instruction [he has]' -- thus. To them, thus petitioning, indeed, [Prajāpati uttered] this...