After you receive the Goddess Sword and activate the Emerald Tablet, you can descend to the surface.
Land in the Sealed Grounds
The sailcloth should automatically come out while you fall, but if you ever need to take out the Sailcloth manually, press B while falling to use your Sailcloth to land without injury. Then Fi will tell you where you are. Continue going along the path and you will encounter Deku Babas. You have to swing your sword in the direction that its mouth is open. Otherwise, the attack won't hurt it. Just try a vertical and horizontal slash and see how it affects each type. You'll soon learn which attacks work on which types.
Continue going along the path, defeat more Deku Babas, then jump down to the ground below. After a cut scene, go ahead and you will reach a door that is sealed with a spell. Your next task is to go to the bottom of the big pit.
Go to the Bottom of the Pit
You can run down to the bottom of the pit if you want to, but there is nothing interesting along the way. Just jump down and use the sailcloth to safely get to the bottom.
You will be asked to use a Skyward Strike on the stone in the center. Get close enough to Z-Target it, then point the Wiimote up and hold it still to charge up your sword, then swing the sword in the direction of the stone. Doing so will activate a bunch of air spouts around the area.
Fi will tell you how to use your sword for Dowsing. Hold the C button, then point at the person or item that you want to find. Choose Zelda. Then move your Wiimote around. You will hear a sound when you are pointing in the right direction. As you get closer, the purple ring in the center of the screen will have an arrow on it. Point toward the arrow until the purple ring is just glowing and there is a rapid dowsing sound. This means that you are pointing straight at the item that you are dowsing for.
Use this to move in the correct direction to reach Zelda. Use the air spouts to float up to the higher levels of the pit. Just walk onto an air spout and you will automatically float up on the sailcloth.
Go Toward Zelda
You will get back to the door that was sealed. That door will unlock, so go through. Save the game at the nearby statue, then look around for a treasure chest. It's to the right of the old woman, down the stairs. There is a Revitalizing Potion inside. This gives you an additional bottle. There is even a fairy in one of the pots here, so if you got a potion earlier, you can use it now even if you don't need it, then catch the fairy, since the fairy will revive you if you die. After it revives you, it disappears, so be sure to look for another fairy if that happens.
Now go upstairs to find a strange old woman. After listening to what she has to say, you will put a beacon on your map where she put the red X. Now you can exit through the door that she unlocks for you. You can look through the crack in the door behind the old woman to see something interesting.
Rescue the Goron
Outside, you find some Bokoblins surrounding a Goron. Go up and attack the Bokoblins. You might need to bash them with your shield in order to get them to drop their defenses. Just thrust the Nunchuk forward to bash with the shield. Swing your sword in the direction that they are not blocking with their swords.
Once you defeat the Bokoblins, the Goron will thank you, and he will talk about the Bird Statue. Soon you will be able to use the statue. Not only can you use it to save, but you can also use it to return to Skyloft. From Skyloft, just return to the column of green light to get back to the surface world. When you do that, Fi will tell you that she can send you back to any bird statue that you found on the surface, so be sure to check on each bird statue that you find. If you want to, you can return to Skyloft now to repair your shield if you need to or buy more equipment.
Look around the area where you saved the Goron to find a cave entrance. Climb up and go through, then press A while standing next to the log, then move the control stick to push the log off the edge. This gives you a shortcut to the Sealed Grounds.
Go to Faron Woods
Head toward the beacon. Climb some vines and go through a hole in the wall. Soon you will be close to the beacon. Roll the log over to the wall, then dash up. Now you can continue on to Faron Woods.