Many athletes want to add muscle, for strength, for contact sports, or to reduce injury risk. The process is slower than social media suggests, and it needs both the right training and enough food.
Reasonable principles:
A modest energy surplus, often around 300-500 kcal a day above maintenance, limits unnecessary fat gain
A gain of roughly 0.25-0.5% of body mass per week is a common target for trained people; beginners may gain faster at first
Protein around 1.6 g/kg a day appears enough for most, with some benefit possible up to about 2.2 g/kg
Progressive resistance training, done consistently over months, is the real driver; sleep matters too
Worked example: a 70 kg athlete aiming for 0.25-0.5% a week is looking at roughly 0.2-0.35 kg per week, or about 1-1.5 kg per month. Over a 3-month off-season, a couple of kilograms of mostly lean mass would be a good result.
Weigh yourself a few times a week and look at the weekly average, not single days.