This puzzle is revealed when you find the piece that goes in the divot in the right wall of the first burial chamber.
What's missing from the wall in the burial chamber?
You've probably figured out that you need to move the cobras around and put them in some specific order. So the next thing you need to do is find out what that order is. And you can find that --
-- in the inner sarcophagus in the burial chamber.
How do I open the inner sarcophagus?
How do I reassemble these parchment scraps?
Once you've reassembled the parchment scraps and decoded the hieroglyphs, you know the order the cobras should go in. It might help to know --
-- that this order starts at the upper left corner, the slot the winged figure is pointing to, and moves clockwise around in a circle.
If that's all you need to know, go for it. You can always press the round button in the middle to reset the puzzle if it gets too messed up.
But if you need more help, here are step-by-step directions to solve the puzzle:
Cobra Puzzle, Amateur
Cobra Puzzle, Master
When you get the cobras in the right order, a door opens in the opposite wall. Fun!
How do I reach the new sarcophagus?