शुचौ देशे प्रतिष्ठाप्य स्थिरमासनमात्मनः। नात्युच्छ्रितं नातिनीचं चैलाजिनकुशोत्तरम् ॥

śhuchau deśhe pratiṣhṭhāpya sthiram āsanam ātmanaḥ nātyuchchhritaṁ nāti-nīchaṁ chailājina-kuśhottaram

In a pure place, established on a fixed seat of his own, neither very much raised nor very low, made of a cloth, a black antelope skin, and kusha grass, one over the other;

In plain words: Krishna describes the meditation seat. It should be in a clean place, firm, not too high and not too low, made of kusha grass (a sacred grass), with a deer skin and then a cloth on top.