Something is true if it accords with reality. In other words a true statement is one which matches the reality it represents. If it is raining and I say, "It is raining." then that is a true statement. When it comes to God, God is the Ultimate Reality and thus the basis for all reality. God knows everything (omniscience). God is truth itself since God knows himself, that is he has the ultimate knowledge (omniscience) of the ultimate reality (God). Therefore God is the Ultimate Truth itself.
Everything good comes from God. God is goodness itself. Everything God created is good because God is good. God never intended evil to happen, but since He created free will, He allowed it to happen. God is so good he can bring good from evil. But evil always remains evil.
“God is infinitely good and all his works are good.” (CCC 385)