We shall find, therefore, in this Bhagavad-gita that the complete whole is comprised of the supreme controller, the controlled living entities, the cosmic manifestation, eternal time and karma, or activities, and all of these are explained in this text. All of these taken completely form the complete whole, and the complete whole is called the Supreme Absolute Truth. The complete whole and the complete Absolute Truth are the complete Personality of Godhead, Sri Krishna. All manifestations are due to His different energies. He is the complete whole. . .
The complete whole is not formless. If He is formless, or if He is less than any other thing, then He cannot be the complete whole. The complete whole must have everything within our experience and beyond our experience, otherwise it cannot be complete.
Introduction to Bhagavad-gita-As-It-Is by Srila Prabhupada.
Among the five topics the material cosmic manifestation is created and annihilated again and again. When we speak of creation, Bible says, God said let there be light and there was light. While it is true that God said and there was creation, there is no explanation as to how the creation came in to being. The Lord need not even say anything, just by his will everything happen.
Quoting from authoritative scriptures will answer the question.
Bramha Samhita says,
Krishna who is known as Govinda is the Supreme Godhead. He has an eternal blissful spiritual body. He is the origin of all. He has no other origin and He is the prime cause of all causes.
Verses 7 & 8 of Brahma Samhita explain that Lord Krishna being completely spiritual does not touch the material nature, but glances towards Maya, which is carried by the cit potency. At creation, Shambu a divine halo of the nature of His own subjective portion [svamsa] appears, which is masculine symbol. Ramadevi, the spiritual [cit] potency, beloved consort of the Supreme Lord becomes the corresponding conceiving potencey, which is the symbol of mundane feminine productivity.
All offspring of the consort of the great lord [Mahesvara] of this mundane world are of the nature of the embodiment of the mundane masculine and feminine generative organs.
The person embodying the material causal principle, viz., the great lord of this mundane world [Mahesvara] Shambhu, in the form of the male generating organ, is joined to his female consort the limited energy [Maya] as the efficient causal principle. The Lord of the world Maha-Vishnu is manifest in him by His subjective portion in the form of His glance.
Srila Prabhupada explains in the The Sri Chaitanya Charitamrita,
The word svanga-vishesabhasa-rupe, indicating the form by which the Lord begets living entities in the material world, is explained herein. He is Lord Shiva. In the Brahma-samhita it is stated that Lord Shiva, who is another form of Maha-Vishnu, is like yogurt. Yogurt is nothing but milk, yet it is not milk. Similarly, Lord Shiva is considered the father of this universe, and material nature is considered the mother. The father and mother are known as Lord Shiva and goddess Durga. Together, Lord Shiva’s genitals and the vagina of goddess Durga are worshiped as the Shiva-linga. This is the origin of the material creation. Thus Lord Shiva’s position is between that of the living entity and that of the Supreme Lord. In other words, Lord Shiva is neither the Supreme Personality of Godhead nor a living entity. He is the form through which the Supreme Lord works to beget living entities within this material world. As yogurt is prepared when milk is mixed with a culture, the form of Lord Shiva expands when the Supreme Personality of Godhead is in touch with material nature. The impregnation of material nature by the father, Lord Shiva, is wonderful because at one time innumerable living entities are conceived.