From the University of Toronto
And St. Anselm also wrote on this subject.
As for me, I say just take a walk in nature and look around. Is it all accidental? Pure chaos?
Oh, it is accidental, huh? Then please explain why mathematics, science and astrophysics all work so perfectly. And even chaos theory may be proven mathematically.
Reality exists in the mind of God.
St. Anselm's proof is easier to digest and understand than Descarte's proof.
After you get through all of these meditations, you might take a peek at Kant and Heidigger. Might take a few years to get through all of that, though.