Celestia and Luna were orphaned as fillies, and lived their lives in poverty and innocence. Then, once Starswirl the Bearded enacted his spell, havoc wreaked in pre-harmonic Equestria, and the two sisters have to save it, beginning a new age. But even after Equestria is saved and harmony begun, there is still much left to happen.
Disclaimer: I don't own My Little Pony. This is solely for entertainment purposes.