What is the Godhead according to this teaching, and how did God the Son become visible?

The Godhead is the invisible Spirit, and God the Son stepped out of that invisible Spirit and became visible. Colossians 1 identifies Him as the image of the invisible God, the Godhead, and the firstborn of every creature, pre-eternal like the Father and Spirit; all members are co-equal.

Les explains that the Godhead is the invisible Spirit out of which God the Son stepped and became visible. In Colossians 1, beginning at verse 15, the text refers to God the Son and the redeeming blood in verse 14. God the Son is the image of the invisible God, the Godhead, the firstborn of every creature, meaning Christ was pre-eternal in His existence just like God the Father and God the Spirit. By Him all things were created in heaven and earth, visible and invisible, whether thrones, dominions, principalities, and so forth. He is before all things, and by Him all things consist or are held together. He is the Head of the Body, the Church, the beginning, the firstborn from the dead, referring to His resurrection. In all things He might have the pre-eminence, for it pleased the Father that in Christ all fullness should dwell. The members of the Godhead are not one above the other; they are all co-equal.

Colossians 1:15

Who is the image of the invisible God, the firstborn of every creature:

How did God the Son become visible?

God the Son became visible by stepping out of the invisible Godhead, which is spirit. Colossians 1 presents Him as the image of the invisible God, the firstborn of every creature. He was pre-eternal in existence, and by Him all things were created, both visible and invisible, and all things consist.