Where are all the yellow-triangle puzzles? What are they for?

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.