Here are some tips if you'd like to build some muscle healthily.
Well, you should:
do intense exercise (do pullups, face pulls, pushups, deadlifts, squats, etc. so you actually build muscle (aim for 6-15 reps in one set. If you can do more, incerase the weight or do a harder exercise variation.) for some reason when I was your age I didn't quite understand this lol);
eat A LOT! Eat high protein, high calorie meals or snacks! Aim to eat as clean as possible. No dirty bulks whatsoever even though it may be easier! When your mother makes a meal, eat as much as you can! Sometimes I even ate so much that I was disgusted by food. Even imagining food was uncomfortable, let alone eating xd. Some foods I recommend: eggs (eat sa much as you can), chicken (breasts, or thighs), cottage cheese (a lot of protein. Mix it with sour cream or Greek yoghurt, add a bit of salt, chives and voila!), oats, rice, buckwheat, nuts (Brazilian nuts, peanuts, almonds and hazelnuts), seeds (sunflower seeds)
I have to add that your main focus is not taste but calories! Focus on getting AS MUCH calories as you can and leave taste behind.
Hope this helps
But remember that you HAVE TO hit the gym HARD! No easy workouts, no "oh, I feel tired, imma stop". Do as hard as you possibly can! So much that your flesh is ripping from your bones (don't take it seriously but you get my point)