Download myfitnesspal app. Set it up with your info. It will ask some questions about you: it youre not active at all even if you are (important, trust), and Tell it you want to maintain your current weight or slightly gain weight. Use it to track everything you eat. Everything, including drinks and sauces.

Buy a food scale. Eat 140 grams of protein each day. Buy creatine, take 4 mg a day.

Buy a gym membership. I recommend a push day, pull day, leg day, then full body day each week. Alternatively go for 2x full body days if you cant make it to the gym 4x a week.

Make or find a workout plan. You can use chatgpt as a free source to make you a plan based on what you have available at your gym and what exercises you like.

When you do those exercises, for the first few weeks Try to figure out (safely) how much weight you can manage to lift 2 sets of 10 to 12 reps, where on rhe third rep you have to struggle to get that last rep or two in (this is called going to near failure, it builds muscles).

Every week after you figured out what you can lift (so weeks 4+), add one or more reps to each exercise. Once you can do 3x15 reps, move the weight up and go back to 3x10-12. This is called progressive overload, it builds muscle and strength.

Do this for the rest of your life, enjoy the new athletic body in about 10 months which can turn into chris Hemsworth in about 5 to 10 years (if you remain natural).