As you walk around the island, you occasionally come across simple puzzle-panels that aren't attached to anything. They all have a single yellow triangle in them, and no matter what solution you give, the puzzle gives a "correct" noise.
I assume they're all connected in some sort of larger puzzle.
There is a way to figure out where these puzzles are in game. I'll give some progressive hints about it so you can try to discover it yourself.
Hint 1:
The game has a built-in map somewhere in the world itself (not the boat map!)
Hint 2:
It's a body of water
Hint 3:
The lake by the town is a map of the entire island
Hint 4:
Bright orange leaves in the lake represent orange arrow puzzles you have not found, dark orange leaves represent ones you've found.
MattRix's answer addresses tracking if you've found all of them but doesn't address what they're for. They're spread out across the island, and as MattRix says, the
lake by the town has orange leaves you can use to track which ones you've found and solved.
What they're for is purely a tutorial on the triangle puzzles. If you put them together, you get a tutorial on how the triangle puzzles work. Once you understand that rule, and get all the lasers,
you can go to the base of the mountain, and solve a triangle puzzle.
This then unlocks the final challenge area in the game. The challenge area itself has another triangle puzzle that leads to
The Challenge, which if you complete it, earns you an achievement.
The orange-triangle puzzles can contain several triangles and not every solution you give is correct as you will see when you encounter new puzzles. They act as a tutorial for something big.
These panels unlock the challenge area near the end of the game.
The yellow-triangle puzzles are basically tutorials for more complex puzzles at the later stages of the game. The same as you're taught mechanics of other puzzles in specific areas by doing enough puzzles in order to understand the logic behind it, these are spread across the map, so by doing more of them you can figure out these mechanics by your self (how they work). If you don't care about statistics and 100% completion of the game, do as much as you need in order to understand rules behind it.
Without knowing the rules of yellow-triangle puzzles, you won't be able to access many hidden places under the mountain (this also includes alternative ending of the game).
Here is the video (spoiler!) demonstrating one of such puzzles near ending.
