Thank you all for your comments.
It is not explained in the game, but the right direction in the looping strings is marked by the sparkles. I thought it was obvious.
Of course you can go off the road, straight to catch the sparkles. That's a valid strategy in this game. But that's risky, because then you must move very fast and accurate, as you lose energy quickly. I think it's difficult to complete all the puzzles doing that.
There are more points if you finish with more time and energy. Maybe in a next version I will add a highscore table so that will be more important for the player.