First and foremost, God is beyond description. Language and Logic and Reason cannot encompass God. We humans are very much limited by whatever is the strength of our Mind/intellect , enormous though it is.
That has not stopped humans from trying to describe God, perhaps because humans are ambitious and also because they love to define and describe whatever engages their mind.
We liken God to the Spider. In Mundak Upanishad it is said that just as the Spider sends forth and draws in the threads of its web from within its body, so does the Universe springs from God. ( Mundak I.1.7) It is hinted here that just as the Spider draws the threads back within its body, God dissolves/withdraws the Universe within himself/herself/itself.
God is the Essence of everything. The Sanskrit word used is Rasa or Juice to describe God." Raso Vai Sah." or God is verily the Juice of the Universe.
In Mundak II.1.1, God is likened to a great Fire from which sparks issue by the thousands and into which they fall back,so are the beings which rise from God and return to him/her/it.
Mundak says further that from God, Food is produced. ( Mundak I.1.8 )
In God are centered all the Worlds and those who dwell on them, yet God is subtler than the subtlest ( Mundak.II.2.2 ).