"The Legend of Zelda: Ocarina of Time" has the hero, Link, get tricked by the evil Ganondorf into allowing him access to the "Sacred Realm" to take over the world. You'll have to use your Ocarina to travel through time to play as both a young and an adult version of Link to make things right. Getting the "Lens of Truth" will require the help of both Links, and following a few steps will get you access to the dungeon where the Lens is located.
Go to Kakariko Village while playing as adult Link. Go to the windmill and talk to the man inside it. Take out your Ocarina while standing next to the man to learn the "Song of Storms."
Use your Ocarina to go back in time and play as young Link. Return to Kakariko Village. Go back to the windmill and play the "Song of Storms." This will drain the water from the well located just outside the windmill.
Jump into the empty well and crawl through the small opening. Look for a skeleton leaning on the wall and walk through an invisible opening next to it to enter a large room. Follow the waterway to the left and go north until you reach a dragon's head decoration.
Use your Ocarina to play the song "Zelda's Lullaby" when you reach the dragon's head to drain the water. Return to where you first entered the large room and jump down into a newly visible small pit. Crawl through the opening to begin the fight with Deadhand.
Approach Deadhand and target him. Wait for him to lower his head to attack you and then attack him with your sword. Continue attacking Deadhand when he lowers his head until he's dead. Open the chest that appears after he's defeated to collect the "Lens of Truth."
The Deadhand fight features four grasping hands that pop up out of the ground. They will try to grab you and hold you in place, but they have a limited range and are easily avoided. If they do manage to grab you just wiggle the analog stick and press "A" to get out of it.