What is the difference between a simile and a metaphor?

1one sharp difficulty presented itself. in the intervening twenty-five years my name had become reasonably well known.2 this being so, my trip demanded that i leave my name and my identity at home.3 i had to go alone and i had to be self-contained, a kind of casual turtle carrying his house on his back.4 with all this in mind i wrote to the head office of a great corporation which manufactures trucks.

Echo act 1 now keep the answers educational.