Mercy, but you are without knowledge.
So the author of the Qur'an thinks Christians believe Part one is God and part two is Jesus and part three is the Virgin Mary.
No wonder you are so confused.
Let me remove your massive confusion.
Qur'aan does not describe Trinity. It simply refutes and condemns it. It tells Christians not to even utter that word.
Qur'aan does NOT SAY that Trinity is made up of God, Jesus and Mary.