Answers
What is the Trinity?
One God, eternally existing as Father, Son and Holy Spirit — not three gods, and not one person wearing three masks. The word is not in the Bible; the teaching is assembled from it: God is one, yet Father, Son and Spirit are each called God, each distinct, and all three are named together in baptism and blessing. Every analogy leaks. It is not a contradiction, but it is a mystery, and a God small enough to fit your head would not be worth worshipping.
Go and see for yourself
Hear, O Israel: The LORD our God is one LORD:
Deuteronomy 6:4
Go ye therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost:
Matthew 28:19
The grace of the Lord Jesus Christ, and the love of God, and the communion of the Holy Ghost, be with you all. Amen.
2 Corinthians 13:14