You are given a Vessel of Light and must defeat the Shadow Insects infesting Faron Woods.
Twilight in Faron Woods
After you kill the three Shadow Beasts, go north and there will be a brief cutscene. Go into the water spring and check on the light floating above it. You will receive the Vessel of Light. You can look at the map to see where the teardrops are. There will be invisible insects that you can use your Sense ability to reveal. Each time you kill one of these insects, you will get a teardrop.
Leave the spring and go north, using your Sense ability to reveal Shadow Insects on the way. After defeating Shadow Insects, wait for the teardrops to float down to where you can reach them.
You can dash against the wall of Coro's hut to make the Shadow Insect fly off of it. Or, you can hold the button to create an energy field and kill the Shadow Insect that way. Afterward, you should walk up the wooden path so that Midna can help you jump into Coro's hut. Once inside, go to the bottom. Use your Sense ability to listen to Coro, who is hiding in a corner. When the Shadow Insects appear, you can use the energy field technique to quickly kill them.
Go back the way you came. Look for a gate, then dig to go through a hole next to it. Kill the Shadow Insects that you find beyond the gate. Then go into the cave beyond the gate. Go through until you are outside.
There are more Shadow Insects here, so use your senses to find them. Dash against the wall if they are sitting on a wall that you can't reach, or use the energy field technique. Then find a ledge that Midna can help you jump from. You will eventually reach a wooden platform in the mist where there are more Shadow Insects.
Continue on, getting more help from Midna to jump farther through the area. There will be a swinging obstacle. Be sure not to jump until the obstacle is out of the way.
After more jumping, you will reach an area with a wooden gate. You will need to dig in the ground to make these Shadow Insects come out. After you kill them, go through the wooden gate.
You will encounter more Shadow Beasts. As before, you need to kill all three at once, or kill one, then kill the other two at the same time. Just hold down the button to create the energy field, and get the Shadow Beasts into the field, then release the button to kill them.
Continue along the path and go across the stone bridge. Use your senses to see a monkey and some Shadow Insects. Kill the insects. These should be the last ones. If not, check your map and go back and kill whichever ones you missed. A cutscene will occur once all the Shadow Insects have died.
Go north from the spring. Talk to Coro, the bushy-haired merchant. He will give you a small key so you can reach the Forest Temple.
You should also buy a bottle of oil from him if you can afford it, because it includes a new glass bottle.
Go back the way you came until you see the locked gate. Check on the gate to open it with the small key, then keep going until you reach the mist. Take out your lantern and walk toward the mist. There will be a cutscene. Follow the monkey, killing any monsters that you encounter on the way.
When the monkey drops the lantern, take it. You can use the bottle of oil to fill it back up. Then go through the wooden gate.
Go to the stone bridge. There will be a cutscene. Attack the armored ghost, then watch the cutscene and follow the instructions.
Afterward, cross the stone bridge, kill the Bokoblins, then use your lantern to burn the spiderweb blocking the entrance. (If you are still out of oil, go south across the stone bridge and get some oil from the bird's shop, then come back and burn the spiderweb.) Go inside.