Just fine, thank you for asking.
The chain transfer power from where it's generated by the pedals to the rear wheel where it can push the bike forward.
The gears on a bike work just like any other set of gears, they allow you to trade power for travel - or the other way around. If spinning the pedals is too easy and you can't crank them round any faster, then a change of gears will make the rear wheel turn more WRT the pedals than before, bringing more resistance to the pedals and more speed to the bike. If turning the pedals is too heavy, then dropping a gear will make the pedals easier to turn on the cost of the rear wheel spinning a bit less for each turn of the pedals
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