In the beginning God created the heavens and the earth. And the earth was without form and void, and darkness was on the face of the deep, and the Spirit of God moved on the face of the waters. (Genesis 1: 1-2)

The first allusion in the bible, we see it at the beginning of its first book clarifying that God and the Holy Spirit are one.
The second reference that confirms the trinity for us when God said, let us make man in our image, according to our likeness, when God says let us make, he says it in the plural and did not address the angels or animals, then ... with whom did God speak?
God does not do anything confusing, he is transparent, in Genesis 1:27, he clarifies who he was referring to when he said "and God created man in his image", as we can see, God did not grasp the image of angels or animals, I create your own image.
When God said let's do it, He meant it; that is, God the Father, God the Son and God the Holy Spirit.
We therefore conclude that there is only one God, but he expresses himself through the three persons of the trinity.