One of the reasons I
didn't start biking for many years was being super intimidated by exactly the types of things you're talking about in this thread,
@Villanelle. Everything I came across online seemed so out of my reach knowledge-wise. Luckily I stumbled onto a local monthly ride for people new to biking, at a slow pace, with ridiculously friendly leaders, learning to ride the city streets, and I was hooked.
I currently know how to do basic maintenance on my bike but I still take it to my shop for almost everything - they'll clean it up for me for pennies while I stand around and chit chat so win-win :) The only thing I really do at home is check the air in my tires, then lubricate my chain in winter, but our weather sucks and the chain will start rusting in two seconds if I don't wipe it down myself after riding in the snow/salt mix.
Since my commute is on or very close to transit lines, I didn't worry too much about being able to change my tires the first six months I rode. My plan was to lock up and ride the bus if I popped a flat. I do carry an extra tube on my bike, though - in case there's someone around that is a fast tire-changer that offers to help. Once I started riding more for fun and longer distances, I made sure I was able to do it so I didn't end up stranded 50 miles away from the city. When you get to that point, I do agree that it's super helpful to practice at home, because if you're anything like me you'll take foreeeeevvvvvver and will probably put the tire on backwards at least once and will have a heck of a time getting the tire back on at all and feel like a total wimp -- until you suddenly get it all right and feel like a total badass. I'm still really really really awful at changing my back tire on my bike with gears.
:)
A lot of the tips here, keep in mind too, are from regular riders who have upgraded their bicycles, so it starts making more sense to be more invested at all the levels (maintenance, clothing choices, etc). I pay a lot more attention to my chain and gears now that I'm riding an expensive bike; I want it to last a very long time. I pay a lot more attention to my clothes now that I ride year-round; I want to be comfortable and not just trying-it-out or I won't want to keep riding. And so forth.
On the flip side, I know we've all seen plenty of normal folks riding a bike in jeans and tennis shoes with a backpack that have never been in a bike shop other than the sport section at a big box store, that get around just fine, so take the information that makes sense to you where you are and save the rest til later ;)