The Trinity is not illogical, it is just beyond human comprehension. Much like a dog trying to comprehend algebra. But we can still grasp certain truths based on Divine Revelation. We understand that Jesus is the Eternal Word of God who became man. In theology, God The Father is the Eternal Thought Who Begot the Eternal Word. And the Truth and Love Between the Two proceeds the Third Person of the Holy Trinity: The Holy Spirit. Three Persons One God.
A human analogy would be the human family which is a reflection of the Holy Trinity. A man and a woman conceive a child. Three persons one family sharing the same human nature.
Since the dawn of humanity every civilization has reasoned the necessity of a creator. But because man is finite, and God is Infinite, different cultures have formulated their own concept of who and what God is; thus the Greeks, the Egyptians, the Aztecs, the Phoenicians, The Vikings, the Hindus, the Native Americans, to the Pygmy tribes on remote islands, have naturally wondered and built concepts with their own imagination mixed with legends superstition and untruths.
The only way for man to truly know Who and What God is, is for God to reveal Himself to man. And that’s the whole point of the Bible: God revealing Himself to humanity, beginning with Abraham, continuing through Moses, and and culminating with His Incarnation in Jesus Christ.
Jesus founded His Church to teach the Truth throughout the ages until the end of time. I would recommend studying the Catechism of the Catholic Church which explains it all.
The Gospel of John begins:
In the beginning was the Word, and the Word was with God, and the Word was God. He was with God in the beginning. Through him all things were made; without him nothing was made that has been made. In him was life, and that life was the light of all mankind. The light shines in the darkness, and the darkness has not overcome it. . . . And The Word became flesh and made his dwelling among us. John 1:1-14*