No one wants to claim that they understand the fullness of what the Trinity is. Mystery is the preferred word.
And just as I can't fathom the entire ocean, I can look upon it, see it's vastness, and appreciate that I am but a man.
The first part in understanding the Trinity, is to recognize who God is, and how we know of Him.
God is a Powerful Spirit. We are aware of this because He let us know by speaking to us. When God speaks, what God says...is who God is.
"In the beginning was the Word. The Word was with God and the Word was God. "
"And God said, Let there be light."
Because we USE words, but God IS His Word, this might create part of the mystery around understanding relationship between God, and His begotten Word. aka, the Son of God. Begotten simply means 'comes from'.
The next part that messes with people, is that God's Word became flesh, and lived on earth as a human. As a man, he set aside his Godly powers. So while he was in earth, he would address God as his Father. He would say things like, 'I don't know, only God knows.' or 'why do you call me good? Only God is good.'
This only makes sense if Jesus is hear as a man. And as the Messiah, it is important to know that his life here, was lived as a man.
The only other part of the Trinity, is the Holy Spirit. The HS is simply the Power of God. Not a separate part of God, like your phone and battery are parts. God and The Power of God are the same thing. The Powerful God Speaks. One Being.
The last part of the mystery of the Trinity is how, at the level of God...these three distinctions, are three distinctions persons. And I have yet to find a way to explain it clearly. So I don't try.