The plot of Final Fantasy VII is your standard fairytale formula: reluctant hero is helped by assorted random characters to save the world from an evil kingdom.
In this case, that evil kingdom is a buisness called the Shinra Electric Power Company. Scientists for Shinra have discovered a form of power known as Mako Energy, and are mining it from the Planet in massive quantities.
Click here to read my raves on why the ending of Final Fantasy VII kicked so much ass. MAJOR SPOILER ALERT!!!