These are my (beginner) notes on physical exercises: covering exercises at home, with no or little equipment, without a diet beyond generally aiming to eat somewhat healthy food. With the aim to be reasonably healthy and in shape, but not bodybuilding or powerlifting.
Regular exercises are suggested by dietary guidelines, CDC, and The Wombles: for an adult, that's at least 150 minutes per week of moderate-intensity aerobic activity (e.g., brisk walking), or 75 minutes of vigorous-intensity activity (jogging, running, etc), along with some strength exercises. Benefits of aerobic exercises are numerous and seem rather neat.
Subjectively, it does appear to work as advertised. Not listed in the Wikipedia article, but another benefit is that fit people tend to look better, and it's easier to pick clothes in that case: they tend to sit better, and even silly-looking ones look fine if a person wearing them is in a good shape. Then there are minor implied niceties, such as being able to run a few floors up the stairs without running out of breath, skipping every other step. The body in general appears to work better, too.
It may seem that it is a dull kind of activity which people engage into in a prison, but people tend to spend plenty of time on other dull activities, which are less useful, while the environment may be not that different from a prison in some cases. Besides, one can not stay focused and work on something fun all the time.
It may be hard to start, similarly to learning anything. People try to avoid both, finding all sorts of excuses; yet it does seem fairly easy once you start, especially once it is a part of a routine. Also as with learning, perseverance is important. It helps that exercising may feel like a computer game with slow XP grinding: somewhat addictive, yielding relatively predictable results after putting time and effort into it, and one may optionally learn its mechanics better to increase the efficiency. While sports, I guess, feel more like games of skill.
One can start by picking a few strength exercises, a cardio workout, and repeating that daily. Preferably while not eating too much of junk food, and maybe combined with some stretching.
For strength training, bodyweight exercises tend to be easy to do at home and without equipment. Squats, plank, push-ups (may be more convenient with handles). Pull-ups and hanging leg raises if you have a bar. Sit-ups if you have something soft to lie/sit on.
For aerobic exercises, also at home and without equipment, perhaps the easiest is just to look up cardio workouts, possibly in a video form, for instance on YouTube: videos are good to learn how to do exercises you are not familiar with yet, and one could use those as a timer (since usually those workouts employ some kind of interval training, apparently). For a timer, wall clock works, though it is less convenient to check while facing the floor; a sound-based timer is better. There are workout music mixes with timers on YouTube, too. No shortage of video workouts with various additional restrictions (standing-only, no jumps, low-impact, for seniors, sitting on a chair).
For nutrition, regular dietary guidelines apply. with a bit more proteins. There are calculators and specialized diet development recommendations, along with all the calorie and macronutrient counting business, but I think one can stay in shape without much of that.
For stretching, it is also easy to find routines on YouTube or elsewhere. Apparently some common stretches are borrowed from yoga (asanas, yoga postures), and yoga as exercise by itself should count as a moderate workout. A related seemingly nice practice is mindfulness.
Wikipedia, WikiHow, ExRx.net, and Verywell Fit provide plenty of information; more can be found elsewhere on the Web.
Clothes should not restrict movement, which is a nice properly of clothing in general. They should not be too tight, should be elastic (especially pants, underpants, socks; for t-shorts it is okay to not be elastic), which usually implies some blend of cotton and synthetic elastic materials (such as elastane; apparently often it is 95/5, but 80/20 for socks). Apparently some workout clothing materials (polyester, Lycra/Spandex/elastane) even provide wicking.
Long hair may interfere with movement and sight, as well as absorb sweat, make it feel even hotter during exercises, and be generally awkward. I'm making a bun, but another option is to braid it.
A secure and simple bun, using just hair ties (no pointy, heavy, or unusual devices), can be made with two hair ties: one is used for a tight ponytail, then the ponytail is twisted to form a bun, and secured with another hair tie, similarly to the first option from "How to Do a Quick and Easy Hair Bun", or "Fitness Hairstyle How to Tightly Secure Your Hair Bun", "How to Tie a “Man Bun” (Without Calling It That)".
A quicker bun is just to pass the hair through a hair tie (a loose ponytail), and then pass it again, without pulling all the hair out (leaving a loop): that's nice for cooking and suchlike, but not secure enough for a workout. That's called "the fold over" in "How to Tie Your Long Hair – For Guys (5-YR. ANNV. EDITION)".
Any bun should be tied tightly in order to hold well.
It is individual and minor stuff that determines how to incorporate exercises into one's routine, but I went for exercising in the morning, and it takes me around 2.5 hours from waking up to getting out of the shower, having done squats, plank, pull-ups, and an aerobic workout, leaving a few more quick sets of strength exercises for the daytime (on the way to get a cup of tea, for instance). Having a breakfast, skimming through Hacker News or other light reading, sometimes doing smaller work tasks, and waiting for the body to wake up, is included into that time.
How long it takes to see exercise results is individual as well, but apparently it's on the order of months (or even weeks, especially in the beginning).