Back when I used to use reddit there was /r/bodyweightfitness that was really good and I believe it’s in line with what you want. It’ll help you get stronger, leaner, and it can even done at home. I haven’t been on the site in years but I remember they had a very good wiki and even an app that helped define a workout routine for you. I would recommend you give it a look. I’d recommend supplementing it with cardio exercises (jogging, biking, etc), to increase your heart health and help you loose any fat that you might want to lose.
General rule on knowing if you’re doing it right, you should feel it in your muscles and not in your joints. There’s plenty of online resources to see how to do exercises properly and even upload videos to get some feedback if you’re comfortable with it. You can also book a couple of sessions with a personal trainer if you are able to.
I’d recommend starting with the basic bodyweight exercises. Push-ups, pull-ups, dips, squats, planks. Those kinds of things. If you’re having trouble doing it unassisted it then do it partially until you can do it fully. Gyms also have machines that can help you do it with weights to make it easier as you build up muscle.
Lifting weights is also a good idea, but just make sure you don’t just do curls and triceps extensions. You need to make sure you do exercises for all your body as all your muscles work together, and if some are more developed than others, it could lead to things like cramps, soreness, and bad posture. This is partly why I recommended the bodyweight exercises in my paragraph above. They’re good at targeting a lot of muscles in each workout.