Look at the world around you!
Look at the world around you: The diversity of landscapes, living creatures and celestial bodies testifies about God’s existence. A (German) proverb says correctly: “From nothingness results nothing.”
Without God and his power of creation nothing would exist; there would be complete emptiness.
Ask God to reveal himself to you!
God exists in a world (a sphere, a dimension) that is normally invisible to us. But you may ask God to reveal himself, i.e. to give you signals of his existence and power. God has promised: “You will seek me and find me, when you seek me with all your heart.” (Jer. 29,13), and: “For everyone who seeks finds.” (Mt. 7,8)
It is crucial to seek God with all your heart. That means: Pray with honesty, seriousness and urgency. For doing so, you should reserve plenty of time, withstand any distraction and ask patiently but insistently for a sign from God.