How do you use the cannon in Zelda the twilight princess?

After you revived Ilia's memory, and got the symbols, you'll return to Kariko to get the cannon. Go to Fyer at his colorful pagoda in Lake Hylia. He'll offer to repair it for 300 rupees. pay the man and gApple your way into the cannon once it's fixed. You'll be blasted to the City In The Sky.