What are all those gears for?

When I was a kid, back in the '50s, my first bike was a typical baloon-tired, coaster-brake job that was pretty much standard. One speed, and you'd get off and push for hills. (Such bikes are still common in many areas of the world)
It was not till I started "serious" cycling that I had a bike with gears that one could change. My first was a Schwinn "Varsity" model that had but a single rear derailleur and five speeds. Very simple, even though this was a "friction" shifter.
I soon upgraded to a decent road bike, the Schwinn "Continental" model. That was about 1974 or so. A typical nicer 10 speed of the period. Again, friction shifters rather than the more contemporary "index" models.
I got pretty good at finageling these shifters, which required that you sort of "feel" the different cogs, and also "trim" the front derailleur a bit either way as it would rub.

There are still those of us who use these devices, but they are pretty much history except for vintage bike fans.
Modern indexed shifting is vastly easier and more convenient. Mountain and Hybrid bikes have either the handy twist-type shifters, or the Shimano-pioneered system with thumb-and-forefinger operated items. Road bikes almost all come with some sort of integrated brake-lever/shifter, which is again simple and accurate.
Most modern bikes come with anywhere from 24 to as many as 30 "speeds" or gear ratios, which should provide a gear for any occasion, from climbing very steep hills to going as fast as possible on the way down.

So, with all this improved technology, I wonder why so many bike riders either can't or don't shift gears hardly at all.
I see this all the time at the university where I work; a student with a modern 24-speed mountain bike will come to a hill and either labor up same in a gear that's obviously way too high, or even get off and push, much as I did in 1952!

I have asked numbers of riders about this. "Why don't you shift down to a lower gear?"

The answer is usually one of two things. First, "it's too hard". Meaning, I suppose, that they haven't figured out how to shift gears. Or, "It worked OK when I got the bike, but it doesn't work anymore." Apparently too busy to take the bike back to the shop for a quick adjustment.

When you buy a new bike, any reputable shop will offer a free "tune-up" 30 days or so after you bought it. That's about as much time as it takes for all the cables to stretch out from new, and that's what's causing the shifting problem. The derailleurs are operated by braided steel cables, and new ones stretch a bit. A quick re-adjustment, and they are generally good to go for a long time. Experienced riders can make these adjustments while riding; a quick quarter-turn of the adjuster on the handlebar lever usually takes care of things.

As to the "it's too hard" complaint....It is a bit intimidating to the novice. 24-30 gears? Which one do I use? Actually, it's pretty simple. Here's the theory of gear shifting:

When you're riding a bike, you have a "cadence" (how fast you spin the cranks) that's efficient and comfortable. Usually, this is just a little faster than what most folks start out with; you have to train a little. For most, this efficient cadence will be from 90-100 rpm. The idea of having all those gears is that you can maintain that 90-100 rpm no matter what you're doing.
Going up a big hill? Your lowest gears will let you "spin" up the hill at that efficient cadence. Going fast on a level road? The higher gears will let you maintain a good speed with little effort.

Far and away the most popular bikes currently are various sorts of "mountain" bikes and their relatives, the hybrids or "comfort" bikes, which all have the same type of components. These bikes are all equipped with from seven (on older models) gears or "cogs" on the back, and three gears (chainrings) on the front.
The way to simplify this is to think of your front gears, the chainrings, as gear ranges. The little bitty gear, the "granny" as we say, is the lowest gear range. You can use it to climb up big hills. The middle ring is for "normal" riding, maybe on slightly rolling roads or terrain. The "big ring", or largest gear, is for going very fast, keeping up high speed on downhills, and so forth.

In the rear, it's the reverse. The littlest cog is the highest gear, and the biggest is the lowest. So, the little "granny" up front and the biggest cog in back is the lowest possible gear. Likewise, the big ring up front and the littlest cog in back is the highest. No one but the strongest riders can turn over such a gear at high cadences on a level road.

So, pick a front gear "range" that suits your conditions. Usually, the middle ring will handle nearly everything. Then, fine-tune your pedalling effort with the rear shifter. Getting a bit hard to pedal? Shift down a couple of gears. Getting too easy? Shift up. Best to shift down a couple of gears before the going gets hard, like right before you get to a big hill. It's much harder to shift while you are pushing really hard on the pedals.

If you do this, and keep the chain clean and properly lubricated, you should be able to shift effortlessly and accurately.