It's complicated, especially if your problem is high body fat percentage. Eating disorders are no joke, but controlling body fat ultimately comes down to controlling energy intake.

If you are just not active, then you start at the beginning. Either /r/fitness or /r/bodyweightfitness have beginner guides and faqs. But there's no easy or short road. You have to consistently put in the work and it's not easy.

If you have medical problems or pain you may need medical advice first, or to fix underlying issues, and those subs will not give medical advice.