So it all starts way back when this kid is born. Then time takes its natural course. But I guess I should start when the game kicks off and not ruin the story for anyone else.
So we start off the story with this spiky haired weird guy jumping off of a train with a big group of guys. The spiky one is named Cloud, the guy with the gun on his arm is named Barret. They are in a building called a Mako Reactor which extracts the energy out of the planet for the use of power and is destroying the planet in the process.
They blow the reactor and go back to a bar and discuss future endeavors to save the planet. That is as much as I am going to tell you will have to play the game and learn the rest for yourself.