Bhagavad Gita Chapter 6 Verse 12
भगवद् गीता अध्याय 6 श्लोक 12

तत्रैकाग्रं मनः कृत्वा यतचित्तेन्द्रियक्रियः।
उपविश्यासने युञ्ज्याद्योगमात्मविशुद्धये।।6.12।।



English Translation - Swami Sivananda
6.12 There, having made the mind one-pointed, with the actions of the mind and the senses controlled, let him, seated on the seat, practise Yoga for the purification of the self.


English Translation of Sanskrit Commentary By Sri Shankaracharya's
6.12 Pratisthapya, having established; sthiram, firmly; sucau, in a clean; dese, place, which is solitary, either naturally or through improvement; atmanah, his own; asanam, seat; na ati ucchritam, neither too high; na ati nicam, nor even too low; and that made of caila-ajina-kusa-uttram, cloth, skin, and kusa-grass, placed successively one below the other-the successive arrangement of cloth etc. here is in a reverse order to that of the textual reading-.
What follows after thus establishing the seat? 
 
Upavisya, sitting; tatra, on that; asane, seat; yogam yunjyat, he should concentrate his mind. To what purpose should he concentrate his mind? In answer the Lord says: atma-visuddhaye, for the purification of the internal organ. How? Krtva, making; manah, the mind; ekagram, one-pointed,by withdrawing it from all objects; and yata-citta-indriya-kriyah, keeping the actions (kriyah) of the mind (citta) and senses (indriya) under control (yata).
The external seat has been spoken of. Now is being stated how the posture of the body should be:


Transliteration Bhagavad Gita 6.12Tatraikaagram manah kritwaa yatachittendriyakriyah;
Upavishyaasane yunjyaadyogamaatmavishuddhaye.


Word Meanings Bhagavad Gita 6.12tatra—there; eka-agram—one-pointed; manaḥ—mind; kṛitvā—having made; yata-chitta—controlling the mind; indriya—senses; kriyaḥ—activities; upaviśhya—being seated; āsane—on the seat; yuñjyāt yogam—should strive to practice yog; ātma viśhuddhaye—for purification of the mind; samam—straight; kāya—body; śhiraḥ—head; grīvam—neck; dhārayan—holding; achalam—unmoving; sthiraḥ—still; samprekṣhya—gazing; nāsika-agram—at the tip of the nose; svam—own; diśhaḥ—directions; cha—and; anavalokayan—not looking