The sixth chapter is the most concretely practical in the book, and it is also where the Gita comes closest to the older meditative literature. It describes a seat that is neither too high nor too low, in a clean place, on cloth and skin and grass; a body held with trunk, neck and head in a straight line, the gaze steady; a mind gathered and made single. It prescribes moderation rather than austerity, and says explicitly that yoga is not for the person who eats too much or too little, or who sleeps too much or keeps awake too long.
The chapter's best known image compares the disciplined mind to a lamp in a place without wind, which does not flicker. The comparison is doing more work than it first appears. A lamp in still air is not being held still by effort; it is simply not being disturbed. The state described is an absence of interference rather than an act of concentration, which is why the chapter spends so much time on the conditions around the practice.
Arjuna's interruption is the honest part. This yoga you describe, he says, I do not see how it can last, because the mind is restless, turbulent, powerful and obstinate, and holding it seems as hard as holding the wind. Krishna does not deny it. The mind is hard to restrain, he agrees, but it can be held by repeated practice and by dispassion, and for someone whose mind is not governed it is hard to attain at all.
The atlas describes this practice; it does not instruct anyone in it. What the chapter prescribes belongs to a living tradition with living teachers, and reading a description is not the same as being taught.