I find the isolation to be self-reinforcing - didn't ever feel so blissful before. I find the propensity for solitude comes from an analytical mind, I spend a lot of time doing high level physics, applied maths, control (etc...), so am used to periods of strong extended focus; conversation doesn't usually call for that sort of focus so can feel weird when I have been consistently lost in work. Drugs do wonders for breaking down barriers tho, socializing is ultimately something everyone should do frequently even if it doesn't seem essential.
Method depends on where you're at now. If you're fat, just diet and increase the amount of cardio you do (walking is easy and ~20% less effective per distance than running). Running is good for keeping weight down and also increasing health; trick with it is consistency, start small and work up. I mostly do bodyweight shit since gyms are closed, and I started with a decent base since I had done running in the past.
As for body weight stuff and just working out in general, doing 3 or so sets of 10 reps and allowing yourself to fail in the last set is a decent enough rule of thumb. Do push ups if you dont have a base, try to get 10 in a set, if you cant do 10 do less than that. Lunges/squats are good for legs if youre starting. Once you can do ~50-60 push ups in a row, you can do more difficult shit like pseudo planche pushups, frog stands... I rate pseudo planche pushups since they use a lot of your upper body.
Lots more I could say, but the jist is just consistency. Eat well, dont eat junk food, try to cook your own shit, and eat mostly lean meat, dairy, rice, pasta, oats, veggies, and fruit. Stick to the exercises, take breaks every couple days if you notice strain.