system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:How do you interpret revolutions per minute (RPM) in the context of driving your car, and what do you need to look out for?

Also, is it bad for my RPM to go up when I go down hills on lower gears, so I don't have to waste my brake pads?
gpt
The RPM is how fast the engine is spinning. If you let it go too low (driving slowly on a higher gear) your engine will stall. And neither should you rev your engine too high, going in to the red of the meter.

And no it's not bad to roll down, again as long as the rpm doesn't go in to the red, just shift up to a higher gear if you need to. Engine breaking is actually good for your fuel consumption. As modern cars will complete stop the fuel to the engine if the car is rolling in gear. So if you plan your driving and use your brake as little as possible it will save fuel.