मम योनिर्महद्ब्रह्म तस्मिन् गर्भं दधाम्यहम्। संभवः सर्वभूतानां ततो भवति भारत ॥

mama yonir mahad brahma tasmin garbhaṁ dadhāmy aham sambhavaḥ sarva-bhūtānāṁ tato bhavati bhārata

My womb is the great Eternal; in that I place the germ; thence cometh the birth of all beings, O Bhârata.

In plain words: Krishna says that the great nature is like a mother's womb, and he places the seed of life into it. From this, all living beings are born.