With nothing else to do, start clicking on the blue flames quickly and they'll merge into one big flame. Click on the flame and carry it around with you, don't worry about letting it go. The flame won't disappear when you let it go.
Now take that flame with you and exit the river the through the log and head to the left. Keep going until you see a large green circular paint on the ground and head towards it.
Head to the right and go forward once you see the cart wheel that's lying in the snow.
Once again move to the right and go forward directly in front of the tree trunk with an axe burried in it.
Now move to the left and you'll find something that looks like an old bunker made of stone and wood. Head inside it to find that it's pitch black.
This is where the flame comes in. Drag the blue frame around the area to find some symbols written all over the place. You can also move left and right with A and D while in here.
I suggest that you write down these sybols and the corresponding dots next to them as you will need these for a puzzle soon.
After getting all the symbols, check the right side of the bunker and you'll find some blood from under a certain part of the wall. Interact with it to reveal a ladder. Now start climbing that ladder.
Once you've left the ladder, head to the right and ignore the crow/raven for a moment. You'll find the last tombstone with the symbol on it. Now go back to the bird.
Click the bird and hold that button. The night raven will then exit from the bird's mouth and fly away, leaving you with the key you so badly need.