Theses kinds of questions have no easy answer. Ive done a lot of my own auto work including an engine swap with a friend years ago. This stuff comes with experience but it helps to grow up with an engineer father with a machine shop. It also helps enormously to have gear head friends and have a life long interest in mechanical workings.
Repairing a car these days is not the same as it used to be but I would start with the basics: maintenance items. As you mentioned, changing a tire is a good first step as it will teach you how to secure and jack up a car *safely*. You should also get familiar with tire pressure, acceptable tread wear and tire rotation. Once the tire is off you'll see the brakes and the suspension components. Disc brake pads are simple to change and a good next step: two bolts, caliper slides off, pop out pads, compress piston, insert new pads, slide and bolt back on, done. Under the hood, there are a few educational and simple maintenance items like checking and changing your: air filter, oil and oil filter, brake fluid reservoir, coolant level, and power steering fluid. The above items are like 90%+ of all garage visits.
These items are all part of various subsystems which make up a car so as you work your way through you will get a feel of what things do. With experience you'll be comfortable with popping the hood and getting your hands greasy. I also want to mention that you can and will get hurt, scrapes, small cuts and bruises are not uncommon, it's rough work at times. Take your time, be safe, wear ppe, and work with someone if you can.