First of all id like to apologize cause im not a fluent english speaker.
When someone asks why you are Catholic and why you believe in God?
I say that I believe that Christ Died for me in the cross, I recognize him as my saviour and all this stuff.
But people often ask me: “Why you are Catholic? You don’t have arguments to support your belief? I mean you just believe that there is a God? But when a scientist believes in one thing he has arguments that supports his visions, you just believe in God, suddenly without any argument, it is blind faith!”
But what arguments is supported our Catholic Faith? I mean we just say we have faith, and that’s it? Or our faith is based in arguments, evidence…?
Proving the Existence of God
There are many " proofs " for the existence of God. None of them are so full proof that no one can object to them. They are more like " convergent and convincing arguments ( Catechism of the Catholic Church, paragraph 31). " These " ways " of approaching God from creation have a two fold departure: the physical world and the human person. "(ibid.para. 32)
From the world, its movement, becoming, contingency, order and beauty. ( ibid, para 32)
From the human person by his openness to truth and beauty, his sense of moral goodness, his freedom and the voice of conscience, and his longing for the infinite and happiness. Through all of which he discerns signs of his siritual soul, which can only come from God. ( ibid, para 32)
“The world, and man, attest that they contain within themselves neither their first principle nor their final end, but rather that they participate in Being itself, which alone is without origin or end. Thus, in different ways, man can come to know that there exists a reality which is the first cause and final end of all things, a reality “that everyone calls God”.”
(ibid, para 35)
“Our holy mother, the Church, holds and teaches that God, the first principle and last end of all things, can be known with certainty from the created world by the natural light of human reason.”( para 36)
But one must realize that " you cannot beat a dead horse " or " you can lead a horse to water but you can’t make him drink. " Don’t waste time on people who are " professional doubters " even if they are operating " on their own. " There is more than one that appears on this forum from time to time. You have given them enough time but each to his own.
Twenty Proofs for the Existence of God
Peter Kreeft
peterkreeft.com/topics-mo…xistence.htm#1
Twenty Arguments For The Existence Of God
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The Argument from Change
The Argument from Efficient Causality
The Argument from Time and Contingency
The Argument from Degrees of Perfection
The Design Argument
The Kalam Argument
The Argument from Contingency
The Argument from the World as an Interacting Whole
The Argument from Miracles
The Argument from Consciousness
The Argument from Truth
The Argument from the Origin of the Idea of God
The Ontological Argument
The Moral Argument
The Argument from Conscience
The Argument from Desire
The Argument from Aesthetic Experience
The Argument from Religious Experience
The Common Consent Argument
Pascal’s Wager
But my favorite argument is from Scripture itself, from the facts, content, and inner coherence, and sublimity of the History of Salvation and continued on after Christ through the founding and growth of the Church and the Magisterium of Catholic Church. A religious phenomenon of over 5,000 years unparalled in the history of mankind. Only God could accomplish such a work.
Also see Part 1 of the Catechism of the Catholic Church
vatican.va/archive/ENG0015/_INDEX.HTM 
