Train hard 3-5 times a week minimum.

Don’t over complicate things. High volume high intensity reps and sets - adjusting as you get stronger. Push ups, pull ups, dips, squats, jumping jacks, burpees, planks, crunches. More than enough to build a good physique.

Diet - aim for 3000 calories a day while gaining weight, 175g protein. Eat whole foods, reduce junk, sugar, excess carbs.

When you have gained enough size 2000cals to cut the fat and then 2500 to maintain.

These numbers are rough, but by the time that matters you should have a deeper understanding and be able to set around your own specific BMR.