From Karanodakshayi Vishnu (Maha Vishnu) all the billions material universes (Brahmandas) originate from the pores of His skin and His breathing.

The Supreme Personality of Godhead and cause of ALL causes expands into the material creation as Maha Vishnu.

Deep inside each Brahmanda universe is a secondary universe where Maha Vishnu expands as Garbhodakashayi Vishnu.

Garbhodakashayi Vishnu resides in His secondary material universe that is surrounded and encased in the greater Brahmanda universe. 

Here we see in painting Karanodakshayi Vishnu who is also known as Maha Vishnu.

As said above, Maha Vishnu expands as  Garbhodakashayi Vishnu who resides deep inside His secondary universe found inside of His Brahmanda greater universe.

From Garbhodakashayi Vishnu Lord Brahma appears and creates the Planetary Systems in each universe within their Brahmanda.

In our material universe inside our Brahmanda, there are 14 Planetary Systems however, in other universes inside their Brahmanda, there can be many more planetary systems based on how many heads their Lord Brahma has.

Some Brahmas have 4 heads like ours while others have 10,20,50,1000, a million or even 10 million heads according to Srimad Bhagavatam. 

So from Maha Vishnu's breathing and from the pores of His skin, all the massive universes (Brahmandas) manifest in one breath.

One breath of Maha Vishnu in human years is 311 trillion 40 billion years which is also the life span of Brahma.

The size of our Brahmanda is 44 quadrillion 444 trillion 444 billion miles in diameter or twice that figure if measured from the outer edge of the universe inside the Brahmanda.

Other Brahmandas are much bigger than ours, all are in different sizes depending on how many heads their Lord Brahma has.

Therefore deep inside each Brahmanda universe, Maha Vishnu expands as Garbhodakashayi Vishnu and from Him Lord Brahma appears from a lotus flower growing from Garbhodakashayi Vishnu's naval who then creates the many planetary systems.

Maha Vishnu expands again to a third Vishnu known as Ksirodakashayi Vishnu (Supersoul or Paramatma) who is within the heart of all marginal living entities (jiva souls).