Very fair! Here’s a longer version of the instructions, if it helps:
The goal is to keep driving (with arrow keys) as long as possible. Clear checkpoints by driving through them before the timer runs out; the game ends when a checkpoint timer reaches 0.
The gauge at the top shows how long you can keep driving. To refill it, you need fish. Hit c to cast your line. When you hear the alert noise and see the “!!” hit c again to reel in a fish.
Casting your line uses the momentum of the car, so the faster you’re going, the further you’ll cast. (I think this is what confuses most people.) You also always fish in the direction you’re driving, so you have to line up the whole car to aim. Bite timing and fish size are random, but if I remember correctly, you’re more likely to get a big fish from deep water (the parts that look choppy).
The only thing the difficulty affects is how much time you have to hit each checkpoint. So you can practice steering and fishing on the lowest difficulty and then increase it as hitting checkpoints gets easier. :)