Sorry, you can't explain these things in a couple sentences. 1 1/2 pages - take it or leave it.
Man and dinosaurs coexisted. Gen. 1 tells us on the 5th day, God made all the sea creatures, then on the 6th day all the animals and man - and God saw that it was GOOD.
Dinos weren't huge in the beginning, small as any young reptiles would be. The interesting thing about some reptiles, they don't stop growing. So as man aged hundreds of years, so did some reptiles, who became huge. Leviaton and Behemoth are mentioned.
No animals were a threat in the Garden. None feared man and vice versa until sin distorted the world and their naturally "good" harmonious behavior was altered. Evil invaded all and so some animals became predators and dangerous. Man subdued these creatures, drove them away from civilization, far away. They probably did not allow these young dinos a chance to grow for hundreds of years, and cut their lives short. But those that migrated far, lived longer and grew bigger. I was there, I witnessed it! kidding. The flood killed them and buried them in mud to preserve their bodies for a few thousands years for us to see. Of course you have to believe in a young earth for this story to make sense. So we must throw all dating methods out the window, they are flawed! The earth and universe are young. Light was given to us instantly, so did'nt take billions of years to get here - but that's another can of worms I don't care to debate.