1) What's up with those bikes with that extra set of handlebars perpendicular to the regular handlebars, the ones that make the cyclist practically lie down in order to grab? Usually used by people all done up in their little stretchy bike outfits who think they're doing the Tour de France but it's really a busy public path...What's the point of those handlebars, and doesn't it make it more difficult to control the steering??
2) On my bike I have two gear shifts: one on the left with 3 gear positions, and one on the right with 7. Yeah, I should have asked years ago when I bought my bike, but hey...in today's economy, who has time? But...what's the purpose of each? TBH, I pretty much have the one on the left permanently set to 3, and of course the one on the right I'm constantly shifting depending on the situation...start off at 1 when I start pedaling and crank it up as I get rolling...
Ideally with a front brake. :)
Bikes with one gear may or may not be in Fixed Gear mode. See:
I mention this because most(?) fixies have a "flip-flop" hub which lets the wheel run in fixed gear mode or with a freewheel.
But to answer your question, in fixed gear mode, the bike stops either when the rider uses a caliper brake with enough pressure to stop the bike, or the rider applies breaking pressure by slowing down the pedaling action. Or a combination thereof.
An alternative method of stopping is to crash into an object which is either stationary, or moving at a slower speed than or contrary direction to the bike's direction of travel.
A third method involves the laws of inertia or momentum, but even I'm not going to sink to that level of pedantry. (at least not yet)
By turning kinetic energy into heat ;)