The Catechism in Questions & Answers

55. What does it mean when we say: “God is the Almighty”?

God can do all things. Nothing is impossible for Him. God’s will and activity cannot be limited by anyone. The creation clearly demonstrates that God is almighty. All things have been created through His word alone. He has created everything that exists— including everything that we human beings can see, and everything that we cannot see—from nothing. It will also be through His omnipotence that the new creation will come into being. God’s omnipotence also includes His omniscience and omnipresence.

New creation: see Question 581.

“But He said, ‘The things which are impossible with men are possible with God’.” Luke 18: 27
“By faith we understand that the worlds were framed by the word of God, so that the things which are seen were not made of things which are visible.” Hebrews 11: 3