The world has ended and fallen apart, you and maybe your friends are the last of your kind and you are determined to survive. The land not long ago had been plagued by war not between man and man but between man and nature. Mother Earth herself decided that humans had harmed her long enough so she brought all the pain to an end. She caused a great earthquake, one which shattered the land and caused lava to pour from the earth, eventually overwhelming the seas. Your survival is up to you, find enough resources to keep you alive and find a nice place to live in. You can also die and let the human race die off in the blink of an eye.
Copy the zipped map file *as is* into your Saves folder. The next time you run Minecraft, the map will appear under your Saved Games.